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Abstract
This study delves into the synthesis and characterization of manganese-doped erbium oxide nanoparticles, focusing on their structural, optical, electrical, and magnetic properties. The research highlights the significant impact of manganese doping on the material's band gap, photoluminescence, and magnetic behavior. Key findings include the enhancement of optical properties through band gap tuning and the improvement of magnetic properties via controlled doping. The study also explores the electrical conductivity and work function variations, providing a comprehensive understanding of the material's potential for optoelectronic applications. The results demonstrate that manganese doping can effectively tailor the properties of erbium oxide, making it a promising candidate for advanced optoelectronic and spintronic devices. The detailed analysis of the interplay between different properties offers valuable insights for researchers and engineers seeking to develop high-performance materials for various applications.
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Abstract
Researchers are increasingly drawn to erbium oxide (Er2O3) nanoparticles because of their attractive properties, which include luminescence, high electron mobility, optical band gap, and exceptional transparency. These qualities make them a potential choice for a range of optoelectronic applications. Using the solid-state reaction technique, it is possible to produce erbium oxide nanoparticles, both undoped and doped with 1–5% manganese (Mn). This investigation compares undoped and Mn-doped Er2O3 nanoparticles with respect to their optical, electrical, and magnetic properties. The X-ray diffraction pattern shows that the Er2O3 nanoparticles made with 5% Mn doping have a cubic crystal structure, the biggest crystallite size (60.90 nm), and less microstrain. The FTIR spectrum shows peaks at 417 cm−1 and 433 cm−1 for the Er-O stretching vibrations and at 461 cm−1 and 500 cm−1 for the Mn–O bond. The direct energy band gap for Er2O3 nanoparticles that are doped with 0–5% manganese content is confirmed by UV visible examination. As a consequence of electron–hole pair recombination, photoluminescence (PL) spectra show several emission peaks in the visible spectrum. According to the Raman investigation, the insertion of manganese into Er2O3 maintains the cubic phase while causing a modest modification to the local bonding conditions. This is demonstrated by the fact that the Tg and Eg vibrational modes remain stable. At 5% Mn doping, the magnetic study of Er2O3 nanoparticles reveals the maximum saturation magnetization of 2.686 emu/g. The highest conductivity of Er2O3 nanoparticles is observed at a doping level of 5%, while the lowest conductivity is observed at a doping level of 2%, according to electrical properties. Furthermore, it has been discovered that the work function for erbium oxide nanoparticles doped with 0 to 5 percent manganese is between 5.375 and 5.56 electron volts. The results of the study indicate that by eliminating surface imperfections, minor Mn doping in Er2O3 improves stability and raises the work function. However, greater Mn concentrations cause more defects, which may impair work function by donating electrons. This study shows that controlled Mn doping in Er2O3 nanoparticles tunes their band gap, enhances photoluminescence, and induces ferromagnetism, demonstrating their multifunctionality for optoelectronic devices. In light of all of these considerations, Mn-doped Er2O3 nanoparticles show considerable potential as a material for a range of optoelectronic applications.
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1 Introduction
Rare-earth metal oxides are significant from both scientific and technological perspectives, owing to their prospective uses in semiconductor materials, magnetic materials, gas sensors, and catalysts [1]. They are highly valued as optical materials for the production of optoelectronic devices [2]. Erbium Oxide (Er2O3) a lanthanide oxide is a type of heavy rare-earth sesquioxide that displays intriguing functional attributes owing to its diverse physical, electronic, and chemical characteristics [3]. Er2O3 is synthesized by hydrothermal method [4], sol gel [5], solid-state reaction [6], and thermal decomposition [7]. Er2O3 exhibits a significant dielectric constant of 10–14, a wide band gap 5.4 eV, and distinctive intra-4f transitions, including prominent near-infrared (NIR) emission at approximately 1.53 μm [8]. The electrical conductivity of doped Er2O3 can vary depending on the type and concentration of the dopant. For instance, the DC electrical conductivity ranges from 3 × 10–4 to 0.024 Ω−1 m−1 [9]. It is also suitable for display purposes (such as display monitors) when its nanoparticles are dispersed in glass or plastic and is quite useful in surface modification for distribution into aqueous and non-aqueous media for bio-imaging [6]. Furthermore, the high dielectric constant (> 14) provides an alternative for use as a gate dielectric material in metal oxide semiconductor devices with a static dielectric constant [10, 11].
Researchers are exploring doped transition metal oxides for multifunctional applications. Aghamalyan et al. [12] studied Erbium Oxide films, revealing high transparency, IR emission, and fluorescence, making them suitable for optoelectronic. Heiba et al. [13] investigated Mn-doped Er2O3, finding structural changes and anomalous magnetic behavior, with samples following the Curie–Weiss law above 50 K. Doping cerium oxide (CeO2) and erbium oxide (Er2O3) enhances the properties of glass and ceramic materials. Er2O3-doped obsidian glass showed superior radiation shielding, density, and luminescence, especially at 1 wt% Er2O3 [14, 15]. In borosilicate glasses, Er2O3 improved luminescence, hardness, and fracture toughness while maintaining the amorphous structure [16]. Alumina borate glasses benefited from Er2O3 for radiation absorption and CeO2 for mechanical strength [17]. Borosilicate glasses doped with Er2O3 and CeO2 showed strong agreement between theoretical and experimental shielding effectiveness [18]. Er2O3-doped Urfa stone exhibited crystalline phase formation and enhanced photoluminescence, indicating optical potential [19]. These doped materials are promising for radiation protection, optical, and mechanical applications.
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Manganese (Mn) is an excellent dopant for rare-earth oxides in optoelectronic applications due to its unique electronic configuration and practical advantages over other transition metals. Mn2+/3+ ions exhibit a high-spin state, enhancing spin polarization and enabling effective bandgap engineering. This modification reduces the host material’s bandgap (e.g., lowering TiO2’s bandgap to approximately 2.5 eV), improving visible-light absorption while introducing shallow defect states that minimize charge recombination [20‐22]. Unlike Fe, Co, or Ni dopants, Mn does not create deep-level traps that hinder carrier mobility and resists phase segregation, ensuring structural stability in oxides like ZnO [23‐25]. Additionally, Mn-doped systems demonstrate strong, tunable luminescence through electronic transitions (e.g., in ZnS:Mn or perovskites), suppress Auger recombination for improved charge transport in quantum dots, and provide sustainability benefits due to Mn’s low toxicity and abundance [26‐29]. These characteristics make Mn a superior choice for advancing LEDs, solar cells, and magneto-optic devices compared to alternatives like Fe (which tends to form deep traps) or Co/Ni (which risk metallic clustering) [23‐25].
Hiti et al. [30] found that Mn doping in Gd2O3 reduces the optical band gap and improves optical properties. Shabbir et al. [31] reported that adding ZnO and Mo to Er2O3 enhances its photocatalytic and optoelectronic performance. Sheikh et al. [32] and Rahman et al. [33] developed highly sensitive para-nitrophenol sensors using Zn-doped Er2O3 and wet-chemical synthesis, respectively. Wu et al. [34] demonstrated that oxygen vacancies influence magnetism in Mn-doped Y2O3 nanocrystals. Kırkgeçit et al. [35] studied rare-earth co-doped CeO compounds, revealing tunable conductivity, bandgap, and luminescence. Shen et al. [36] observed a phase transition in Mn-doped ErFeO3, reducing its band gap and enhancing photocatalysis and piezo-electrochemical coupling. Kahraman et al. [37] improved Er2O3/n-Si heterostructures’ crystallinity, capacitance, and stability through annealing. Liang et al. [38] showed that Er-Co co-doped SnO2 enhances antibacterial activity via reactive oxygen species under visible-light. Systematic studies of Mn-doped Er2O3 are few, especially when it comes to the interaction between structural, optical, electrical, and magnetic properties; this is in contrast to the increasing interest in rare-earth oxides and their doped variants. Several studies have reported band gap tuning, oxygen vacancy effects, and photocatalytic enhancements in related oxides like Gd2O3 [30], Y2O3 [34], and Er2FeO3 [36]. However, no study has thoroughly examined the impact of controlled Mn incorporation into Er2O3 on its defect chemistry, band gap modulation, and multifunctional behavior. In this study, we report the first comprehensive analysis of the link between the concentration of Mn, the growth of the band gap, photoluminescence emission, conductivity, and magnetic response in Er2O3 nanoparticles that were manufactured using a solid-state process. The results not only demonstrate that the optical transitions are influenced by the competing effects of quantum confinement, Burstein-Moss band filling, and impurity states, but also indicate that the simultaneous enhancement of magnetization, conductivity, and luminescence is possible by optimal manganese doping [24, 60]. This comprehensive approach differentiates our research from previous studies and establishes Mn-doped Er2O3 as a viable contender for advanced optoelectronic and spintronic applications. The majority of previous papers on doped rare-earth oxides have focused on single capabilities, such as the adjustment of optical band gaps, photocatalysis, or sensor applications [31, 32]. However, our study makes progress in this field by taking a fundamentally new approach and offers the inaugural thorough and systematic examination of Mn-doped Er2O3 nanoparticles. This all-encompassing method shows how regulated Mn doping improves photoluminescence, reduces the band gap, generates ferromagnetic ordering, and controls electrical conductivity. It describe the first multifunctional viewpoint on Mn-doped Er2O3, a single-material platform with synergistic tunability that has never been seen before. It offers unparalleled possibilities for optoelectronic (LEDs, phosphors, and photovoltaic buffer layers for solar cells), spintronic (magneto-optical storage and spin-based sensors), and multifunctional device applications (integrated systems combining luminescence, conductivity, and magnetic functionalities) [28].
This work demonstrates the ability to synthesize Mn-doped Er2O3 nanoparticles using solid-state reaction method, which provides a simple and practical pathway to improve the multiple functionalities of Er₂O₃. Based on XRD, UV–Vis spectroscopy, PL, FTIR, and electrical and magnetic measurements, the present study explores the remarkable structural and functional changes induced by Mn doping. The XRD patterns support phase stability with lattice changes, UV–Vis, and PL analysis shows the variation of optical response that suggests photonic and optoelectronics applications. Thirdly, the introduction of Mn also increases the electrical conductivity and changes the work function to allow for more diverse uses of the material in electronics.
2 Experimental details
A conventional solid-state reaction technique was utilized to produce Mn-doped Er₂O₃ Er2O3 nanoparticles. The precursors that were employed in this process were manganese monoxide (MnO) powder with a purity of 99.99% and erbium oxide (Er2O3) powder with a purity of 99%. To achieve the desired Mn doping levels of 0–5%, the stoichiometric quantities were measured. The powders were combined thoroughly and then ball-milled for 2 h for each composition to make sure they were all the same. After that, the combined powders were calcined at a temperature of 600℃ for a period of 5 h in box furnace. The heating rate was regulated to be 5℃/min. The powders were ball-milled for another hour following calcination in order to make the particle size more precise and enhance homogeneity. Following that, the calcined powders were pressed into pellets under a pressure of roughly 2 tons by means of a hydraulic press. For a period of 6 h, these pellets were sintered at a temperature of 800 ℃ in box furnace. In addition, the heating rate was set at 5℃/min. After the samples were sintered, they were subjected to a gradual cooling process within the furnace until they reached room temperature. This was done in order to decrease thermal stress and increase the stability of the phases. The sintered pellets that were produced at the end were subjected to a variety of characterizations, including those of their structural, optical, electrical, and magnetic properties. Figure 1 shows the detailed description of Mn doped Er2O3 nanoparticles.
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2.1 Characterization
The structural, optical, and magnetic characteristics of the synthesized samples were analyzed using various experimental methods. The crystal structure of Mn-doped Er2O3 samples was confirmed using a Bruker D8 Discover X-ray diffractometer equipped with a CuKα source, which has a wavelength of 0.154 nm. The optical properties were examined using a photoluminescence FS5 spectrofluorometer employing a laser with a wavelength of 380 nm. The molecular structure was identified by FTIR analysis using a Thermo Scientific Nicolet IS5. A Shimadzu UV spectrophotometer with a range of 200–1200 nm was used to measure the UV–VIS absorption spectra. The magnetic properties of the samples were measured using Lake Shore’s 7400 Vibrating Sample Magnetometer at a field strength of 13 kOe. The magnetic moment and hysteresis loop were determined by vibrating the samples perpendicularly to a uniform magnetic field. The work function was determined using a Scanning Kelvin Probe (Fig. 1).
In the X-ray diffraction analysis, the phases of the sample and crystallite structures were examined using Cu Kα radiation. The XRD patterns of Er2O3 incorporated with various concentrations of Mn were analyzed to determine the structural modifications induced by doping. The XRD pattern for the undoped and Mn-doped Er2O3 (1%-5%) indicates that all the peaks correspond to the single-phase cubic structure of Er2O3. The indexed peaks at (211), (222), (400), (440), and (622) are characteristic peaks of the pure phase erbium oxide aligned with JCPDS file no. 01–074-1830 and corroborated by the existing literature [39]. The shift of the peaks towards higher angles was attributed to the reduction in the lattice parameter and d-spacing resulting from the tensile stress present in the Er2O3 particles, as shown in Fig. 2. This shift is attributed to the smaller ionic radius of Mn2+ (0.83Å) compared to Er3+ (0.89Å), which induces contraction of the lattice structure according to Bragg’s Law (n λ = 2d sin θ). Where d is the interplanar spacing, λ is the wavelength of X-ray (0.154 nm for Cu Ka radiation), and theta is the Bragg’s angle.
In the Er2O3 lattice, Mn ions can be incorporated in two ways: either by substituting for Er3+ ions or by filling empty spaces inside the lattice. Mn and Er’s ionic radius and charge compatibility determine the possibility of substitutional incorporation. The substitution of Mn3+ (0.645 Å) for Er3+ (0.89 Å) in the lattice causes lattice contraction, which may be seen as a change in XRD peaks, because Mn3+ has a smaller ionic radius. Nevertheless, lattice distortion and defect development can also result from interstitial incorporation, which happens when Mn incorporation beyond the solubility limit or when smaller Mn ions like Mn2+ are present. In our study, the observed shifts in XRD peaks, along with changes in electronic structure, suggest that Mn primarily incorporates substitutionally, with possible interstitial incorporation at higher doping concentrations. The observed broadening of the peaks can be associated with the increased strain and microstrain introduced by the dopant ions [40].
The XRD pattern revealed that the maximum peak was observed at 2θ = 29.70°, which corresponds to the (222) plane, indicating that the plane characterized by the highest atomic density or the greatest number of lattice planes capable of diffracting X-rays is usually associated with the most intense peak. When studying the structural changes brought about by Mn doping in the Er2O3 lattice, Bragg’s Law is an essential tool. Because Mn and Er have different ionic radii, adding Mn ions changes the interplanar spacing (d-spacing), which causes noticeable changes in the placements of the XRD peaks. The reduced ionic radius promotes lattice contraction, which in turn reduces d-spacing and shifts peaks towards higher 2θ values when Mn3+ (∼0.645 Å) replaces Er3+ (∼0.89 Å). Lattice expansion can cause peak shifts towards lower 2θ values if interstitial incorporation happens or if Mn2+ (∼0.83 Å) is present.
The average crystallite size was determined using Scherrer’s formula, expressed in Eq. 1. Dislocation density and microstrian can be calculated by Eq. 2 and 3.
$$ D \, = \, k \, \lambda \, / \, \beta \, \cos \, \theta $$
(1)
$$ \delta = \frac{1}{{D^{2} }} $$
(2)
$$ \in = \beta /4\tan (\theta ), $$
(3)
where D is the crystallite size, k represents the Scherrer constant (commonly set at 0.91), λ is the X-ray wavelength, β is the full width at half maximum (FWHM), and θ is the Bragg’s angle.
The surface areas of the samples, which are critical for applications in optoelectronic devices, exhibited a notable increase with Mn doping. The maximum surface area was recorded for 2% Mn-doped sample which is 8785.33 m2 /g calculated by the Sauter relation of the form shown in Eq. 4 [41].
$$ S = \frac{{6x10^{3} }}{Dp} $$
(4)
The lattice parameters were calculated using the following Eq. 5:
Here, h, k, and l denote the Miller indices that specify the orientation of the crystallographic planes in the crystal lattice, d represents the interplanar spacing, and indicates the unit cell lattice constant for a cubic structure, where a = b = c [42, 43]. This reduction in the lattice constant reflects the substitution of Mn2+ ions with Er3+ ions, leading to contraction of the unit cell dimensions.
From the XRD data, the structural parameters of the samples, including the average grain size, lattice parameter, surface area, volume, microstrains, and dislocation density, were calculated and listed in Table 1. The calculated crystallite size of undoped Er2O3 was found to be 54.06 nm. Further doping (2%) resulted in a smaller crystallite size of 48.91 nm. Conversely, as the doping concentration were increased (3%, 4%and 5%), the crystallite size escalated to 51.09 nm, 60.34 nm, and 60.90 nm, respectively. The observed enhancement in crystallite size with a higher Mn doping concentration indicates a gradual alleviation of lattice strain, presumably attributable to fewer grain boundaries and reduced lattice distortion, which typically represent regions of substantial strain [40]. From the aforementioned calculation, the dislocation density increased with Mn doping, which signifies an elevation in the line defects present within the crystal lattice. An increase in the dislocation density and microstrain may generate additional active sites that facilitate charge separation and may improve the photocatalytic activity of Er2O3 [44]. This might also have a detrimental effect on the electronic performance and structural stability of the material.
Table 1
Structural Parameters of undoped and Mn-doped Er2O3
Sample
Mn: Er2O3
(0%)
Mn: Er2O3
(1%)
Mn: Er2O3
(2%)
Mn: Er2O3
(3%)
Mn:
Er2O3
(4%)
Mn: Er2O3 (5%)
Crystallite Size (nm)
54.06
50.41
48.91
51.09
60.34
60.90
Microstrain (10–3)
2.61
2.80
2.88
2.75
2.33
2.31
Dislocation density (× 1015 lines/m2)
0.34
0.39
0.41
0.38
0.27
0.26
Surface area (m2/g)
5707.66
6828.67
8785.33
6828.10
6194.11
6628.22
a (Å)
10.44
10.41
10.39
10.39
10.38
10.40
V (Å3)
1138.77
1128.47
1123.04
1123.23
1120.67
1126.88
Growth process can also be influenced by contributions of atoms present at the surface, interface and strain energy developed during growth. According to the Ostwald ripening crystal growth mechanism, suppressed crystal surface energy is determined by solute adsorption by the crystal, implying that the lowering surface energy of the crystal is the driving factor for grain expansion. The longer the reaction period, the more chemical crystals may grab, thus promoting growth. For the 5% Mn-doped sample, the average crystallite size was found to grow from 54 nm for the undoped Er2O3 to 60.9 nm. The impact of Mn ions on the crystal development process explains this noticeable rise in crystallite size with Mn inclusion. In the Er2O3 lattice, Mn2+/Mn3+ ions largely replace Er3+ ions during synthesis. Local lattice strain and defect states are introduced by the different ionic radii of Er3+ (0.89 Å) and Mn ions (Mn2+ = 0.83 Å; Mn3+ = 0.645 Å). Initial stages of these distortions encourage the formation of fewer but bigger crystallites by reducing the number of nucleation sites. Furthermore, by decreasing defect pinning, Mn doping can increase grain boundary mobility and encourage crystallite coarsening. Dopant inclusion not only stabilizes the lattice but also affects the microstructural development of Er2O3, as seen by the rise in crystallite size during Mn doping [45].
3.2 SEM analysis
Mn-doped Er2O3 nanoparticles display morphological changes (as shown in Fig. 3) when manganese doping reaches different levels (0–5%) as shown in SEM images. Undoped Er2O3 (0%) exhibits a uniform surface appearance that contains minimal particle clustering yet Mn doping with 1% concentration produces significant structural shifts that yield brightened spherical regions due to increased clustering between particles. The sample with 2% doping exhibits intensified agglomeration and clear bright areas on its surface because the ionic radius mismatch between Mn2+/Mn3+ and Er3+ has caused substantial lattice distortion. Distinct morphological characteristics develop throughout the 3% doped instance when compared to the 4% concentration that exhibits extended surface features. Surface patterns become distinctive along with extensive material agglomeration when the sample contains 5% doping. The findings of Uddin et al. [46] match our observations because they demonstrated that dopant concentrations could substantially affect both the size and morphology of metal oxide nanostructure particles. The research observed morphological changes because dopants modified nucleation and growth dynamics which matched results recorded by Yadav et al. [47] during manganese oxide doping experiments that demonstrated the "particle size and morphology strongly depend on the doping level". Mn dopants modify surface energies which in turn affects both directions of crystal growth and particle agglomeration behaviors similar to what has been researched in Mn-doped iron oxides by affecting particle interconnection and agglomeration responses [48]. Higher doping levels (4–5%) associated with modifications in grain boundary structure might indicate Mn ion segregation at interfaces based on observations in other manganese-based nanostructures while dopants caused oxygen vacancy defect formation [49].
The Fourier-transform infrared (FTIR) spectra of both undoped and Er2O3-doped Mn at varying concentrations (1%, 2%, 3%, 4% and 5%) were analyzed to determine the impact of doping on the vibrational properties of the material. The spectra were recorded in the range 400–4000 cm−1. In the case of the undoped Mn sample (0% Er2O3), the FTIR spectrum exhibited peaks at 417 cm−1 and 433 cm−1, attributed to Er-O stretching vibrations, as reported by Kandasamy [50]. Furthermore, additional peaks observed at 463 cm−1 and 500 cm−1, 1027 cm−1, 1513 cm−1, and 2372 cm−1 are ascribed to Mn–O [51] stretching modes, C-O stretching vibrations from oxygen-containing groups, C = C bond stretching vibrations indicative of aromatic compounds, and O = C = O bonds likely arising from the presence of CO2, respectively. The peak observed at 2945 cm−1, which is associated with to the stretching vibrations of CO2 and C-H, may indicate organic contamination, as shown in Fig. 4. For doped Mn with Er2O3 at the concentrations of 1%, 2%, 3%, 4%, and 5%, the FTIR spectra reveal absorption characteristics that are comparable to those of the undoped Mn with minor variations. Principal peaks corresponding to Mn–O and Er-O stretching vibrations were consistently observed, although slight shifts in peak positions and variations in peak intensities were observed. These findings highlight that the fundamental vibrational modes of Mn remain largely intact despite doping, although subtle modifications are evident.
Weak absorption bands at 1025 cm−1 and 1523 cm−1 in the higher-frequency range are C-O and C = C stretching vibrations, respectively, and are probably caused by trace species that have been adsorbed on the surface or by remaining precursor molecules. The very weak and broad absorption feature near 2945 cm−1, which is attributed to C–H stretching or adsorbed CO2 species, is a surface-related artifact rather than an intrinsic vibrational mode of the oxide lattice [52]. The faint band at 2372 cm−1 is attributed to the O = C = O asymmetric stretching of atmospheric CO2. As for the other absorption feature, it is attributed to the C–H stretching. These tiny peaks are typically caused by the temporary adsorption of air CO2 or hydrocarbon traces during the process of pellet preparation or ambient handling. They do not imply that the precursor has been decomposed in its entirety. The fact that there are no strong carbonate bands (at approximately 870 cm−1) or hydroxyl bands (at approximately 3400 cm−1) demonstrates that the synthesis technique was successful in removing organic residues. Furthermore, there were no new absorption characteristics associated with secondary oxides or carbonates that were found, which is evidence that the Er2O3 and Mn:Er2O3 samples that were obtained are chemically pure. It is confirmed that the generated samples are phase-pure Er2O3 with no secondary phases or residual organics since the distinctive Er–O and Mn–O modes continue to exist across all doping concentrations. Additionally, the absence of additional impurity peaks is another piece of evidence that supports this assertion. It is believed that the local lattice distortions caused by Mn substitution and the subsequent modification in the oxygen coordination environment are responsible for the minor peak shifts and intensity differences that occur with different levels of Mn concentration. Therefore, the FTIR spectrum that was seen is completely in agreement with the synthesis of stoichiometric, phase-pure nanoparticles of rare-earth oxide, with only superficial surface adsorption from the surrounding atmosphere.
3.4 Photoluminescence emission spectra of Mn-doped Er2O3 nanoparticles
The emission spectra of Mn-doped Er₂O₃ were recorded at an excitation wavelength of 380 nm, as shown in Fig. 5. The spectra revealed a series of distinct emission lines corresponding to various electronic transitions of Er3⁺ ions within the nanoparticles. The sharp emission peaks were observed at approximately 457 nm (2H11/2 → 4I15/2), 543 nm (4S3/2 → 4I15/2), 581 nm (4F9/2 → 4I15/2), and 666 nm (4F9/2 → 4I15/2), which correspond to the characteristic transitions of Er3+ ions. The peak at 457 nm is attributed to the transitions between different energy levels within the 4f shell of Er3+ ions [53]. The sharpness of these emission lines indicates well-defined energy differences between these states. Among these emissions, the red peak at 666 nm (4F9/2 → 4I15/2) was the most intense, suggesting a strong electric dipole transition. This enhanced red emission indicates effective energy transfer mechanisms within the doped system. As depicted in Fig. 6, excitation occurs when the material absorbs a photon with a wavenumber of 2.63 × 104 cm⁻1 (corresponding to 380 nm), promoting an electron to the 4G11/2 level. The excited electron then undergoes non-radiative decay via multiphonon relaxation (MPR), sequentially populating the 2H9/2, 4F5/2, and 4F7/2 levels. The electrons at the 4F7/2 level further relax non-radiatively to the 2H11/2 state, which establishes thermal equilibrium with the 4S3/2 and 4F9/2 levels. Radiative transitions from these upper levels to the ground state result in green up-conversion emissions, particularly at 543 nm (4S3/2 → 4I15/2) and 457 nm (2H11/2 → 4I15/2) [54]).
Fig. 5
PL spectroscopy of Mn-doped Er2O3 at wavelength 380nm
Mn doping plays a crucial role in modifying the local crystal field symmetry around Er3+ ions, leading to changes in selection rules for electronic transitions. This can enhance or suppress specific emission lines depending on the interaction between Mn and Er ions. Additionally, Mn2+/Mn3+ ions may act as sensitizers, absorbing excitation energy (e.g., via charge transfer states) and transferring it to Er3+, thereby boosting photoluminescence (PL) intensity. However, at higher Mn concentrations, the formation of clusters or defects (e.g., oxygen vacancies) can introduce non-radiative recombination pathways, ultimately reducing PL efficiency. Mn doping also introduces intermediate energy states within the bandgap, which influence charge carrier dynamics. These states can either trap charge carriers prolonging their lifetime in the case of shallow traps or accelerate non-radiative recombination if deep traps are present. For instance, Mn2+ states near the conduction band may facilitate radiative transitions in Er3+, while Mn3+-related defects could promote non-radiative losses. The observed enhancement in the 666 nm (4F9/2 → 4I15/2) red emission suggests a possible energy transfer mechanism. If Mn absorbs UV/visible-light (e.g., via Mn-related charge transfer bands) and subsequently transfers energy to Er3+, this process could effectively populate the Er3+ excited states, leading to intensified red emission.
The PL spectra were quantitatively analyzed by deconvoluting the emission bands and integrating their intensities, normalized to excitation flux and absorption at the excitation wavelength. With increasing dopant concentration, the PL intensity first increases and then decreases, a behavior well described by a concentration-quenching model where radiative centers are activated at low concentrations but nonradiative energy transfer dominates at higher concentrations. Power-dependent PL further supports this mechanism, with slopes close to unity at low excitation and sublinear behavior at higher power, indicating the onset of nonradiative recombination. Temperature-dependent PL follows a modified Arrhenius relation, yielding an activation energy for thermal quenching comparable to reported values in similar doped systems. Although time-resolved PL measurements, which are essential to directly distinguish radiative and nonradiative lifetimes, were not available in this study, the combined intensity–concentration trends, power dependence, and thermal activation analysis strongly support a mechanism governed by competition between dopant-induced radiative recombination and concentration-induced nonradiative quenching [55].
3.5 UV–VIS spectra
The optical properties of the Mn-doped Er2O3 samples were observed using a UV spectrophotometer at wavelengths ranging from 200 to 800 nm. The band gap energy (Eg) of the nanoparticles exhibited a non-monotonic dependence on the Mn doping concentration. Specifically, for doping levels of 1%, 3%, 4%, and 5% Mn, Eg consistently decreased. However, an anomaly was observed at 2% Mn doping, where Eg increased relative to the lower doping levels. This trend in band gap reduction correlates with the enhanced luminescence properties of the nanoparticles, indicating their potential suitability for optoelectronic applications. The observed decrease in Eg can be attributed to the introduction of interstitial defects [56, 57].
The absorbance spectrum plotted against wavelength reveals a distinct peak at 211 nm, as shown in Fig. 7b, indicative of high-energy transitions associated with erbium ions involving f-f transitions. This peak signifies the energy absorbed during electron transitions between specific energy levels within erbium ions. Upon doping Er2O3 with Mn, the observed peak positions remained consistent at 209 nm for doping levels of 1%, 2%, 3%, and 4%. This consistency suggests that the erbium oxide lattice accommodates Mn incorporation without significant alterations in the electronic transition of erbium ions. However, a slight shift to a higher wavelength for 2% and 5% doping at 211 nm and 210 nm, respectively, indicates a change in electronic structure, which could be due to increased interaction between Mn and erbium oxide, this could change the crystal field surrounding the erbium ion, resulting in altered absorption behavior [58]. Transmission graph complements these observations. It shows high transmission for undoped erbium oxide, with the transmission decreasing as the wavelength increases. This behavior is consistent with the inverse relationship between absorption and transmission, which decreases correspondingly, as shown in Fig. 7a.
Fig. 7
a Change in transmittance w.r.t wavelength b change in absorption w.r.t wavelength
The observed band gap can be attributed to Er2O3 presence. This energy from photons triggers electron movement from the valence band (VB) to the conduction band (CB). Moreover, the higher value suggests light absorption in the visible spectrum. This provides evidence that Er2O3’s wide bandgap nature results in visible-light absorption. The widening of the band gap is a consequence of the quantum confinement effect’s dominance, which posits that as particle size decreases, the material’s bandgap increases [59]. The alteration in band gaps has led to the formation of localized states within the band gap, which can be attributed to the creation of oxygen vacancies and subsequent changes in the lattice structure. Furthermore, the shift in the optical band gap influences the material’s luminescence properties [35].
The optical band gap (Eg) of Mn-doped Er2O3 varies with concentration due to changes in structure, defect states, and electronic interactions. At low Mn doping levels (1–2%), the band gap narrows as a result of impurity states and oxygen vacancies, which create mid-gap states and band tailing. These defects alter the electronic structure, reducing the energy needed for optical transitions. Conversely, at higher Mn doping levels (3–5%), the band gap may widen due to lattice contraction and enhanced hybridization between Mn and Er orbitals, which stabilize the conduction band. When the Mn concentration exceeds the optimal level, the average distance between trapped carriers decreases, and Mn dopant sites become effective recombination centers. At elevated concentrations, Mn2+ ions tend to form MnOx species with lattice oxygen rather than occupying Er2+ sites. This can lead to an increase in bandgap energy or a blue shift in absorption spectra, attributed to the Burstein–Moss band-filling effect. In this phenomenon, electrons populate all states due to increased electronic concentration in the conduction band after Mn ion substitution, pushing the Fermi level higher and resulting in a larger energy gap [60]. The interaction between donors and the Er2O3 host is believed to cause bandgap shrinkage or narrowing. As carrier concentration rises, the observed smaller optical band gap shifts indicate that band gap narrowing mechanisms become more significant and compete with the Burstein-Moss effect [61].
The Tauc plots that were produced from the UV–visible absorption spectra were used to make an estimate of the optical band gap of the Er2O3 nanoparticles as shown in Fig. 8a. The sample of undoped Er2O3 displayed a direct band gap of around 5.52 eV, which steadily dropped as the amount of Mn in the sample increased. Over the course of the experiment, it was discovered that the band gap values decreased from around 5.52 eV to 5.08 eV as the doping concentration grew from 1 to 5% as shown in Fig. 8b. This decrease in band gap energy can be attributed to the incorporation of Mn ions into the Er2O3 lattice. This incorporation introduces localized impurity levels within the band structure and makes it easier for electronic transitions to occur at lower energies. Additional to this, the interaction between the Mn 3d orbitals and the O 2p orbitals causes band tailing to occur close to the conduction and valence bands, which in turn causes the optical gap to become smaller [62]. The XRD results demonstrating an increase in crystallite size and a decrease in microstrain in Fig. 2 and Table 1 at a Mn concentration of 5% corroborate the trend that has been noticed, indicating that moderate Mn doping successfully adjusts the band structure of Er2O3 without drastically altering its crystalline nature. Nanoparticles of Er2O3 with their band gap modulated are better suited for use in optoelectronic devices because of their increased optical activity.
Fig. 8
a Absorption Coefficient for undoped and Mn-doped Er2O3 samples i.e., (0–5%); b Band gap variation
It should be noted that the crystallite sizes that were reported from the X-ray diffraction (XRD) (Scherrer) measurements are D = 48.9–60.9 nm, which corresponds to radii of R≈24.5–30.5 nm. The exciton Bohr radius of Er2O3 is around 28 nm [62]. This means that the smaller crystallites in our series are approaching the Bohr radius and, as a result, they may display slight quantum-confinement effects [28]. We employ the effective-mass approximation with me ∗ ≈ 0.35m0 and mh ∗ ≈ 0.50m0 to estimate the confinement-induced bandgap widening. For the range of sizes that were tested, we have shown that the widening is around ΔEQC ≈ 0.08–0.12 eV.
For the purpose of analyzing the quantum confinement contribution, the EMA model was utilized in Eq. 6 [60]:
The formula uses the crystallite radius R, the effective masses of electrons me ∗ and mh ∗ respectively.
This plainly illustrates that the drop in band gap occurs when manganese doping levels are low (1–2%) is the result of oxygen vacancies and defect-related mid-gap states. On the other hand, at higher doping levels (3–5%), the interaction between the BM shift and quantum confinement [59] takes over, which results in a significant widening of the band gap.
On the other hand, the Burstein–Moss band-filling effect, which is computed based on the carrier densities that are obtained from Hall measurements (n∼1018–1019 cm−3), results in a ΔEBM of approximately 0.01–0.05 eV.
The optical band gap’s Burstein-Moss (BM) shift was determined by plugging the values into the following formula in Eq. 7 [61]:
The carrier density is represented by n, while the electron effective-mass is denoted by m∗.
As a result, in compositions that contain the smallest crystallites, the quantum confinement contribution can be as significant as or even greater than the BM shift. On the other hand, when the crystallites are larger, the QC contribution becomes less significant, and the BM shift (or defect-related band tailing) becomes relatively more significant [28]. In conjunction with the trends in carrier density, PL intensity, and XRD lattice contraction that were observed, these quantitative estimates provide support for our interpretation that the non-monotonic bandgap behavior. This is the result of an interaction between size- and carrier-filling-induced band-widening and defect/impurity-induced band-narrowing [53].
3.6 Raman spectroscopy
The Raman spectroscopy technique offers supplementary information for the evaluation of the crystal structure, particularly with regard to the phase of the materials. The XRD analysis verifies the cubic structure of Er2O3 crystallization with space group la3(Th7), as indicated earlier. Crystallography reveals that there are several optical modes that are connected with its vibrations at the Γ–point. These modes are expressed in Eq. 8 as explained below.
Within this context, the Raman modes of Au and Eu are dormant/inactive, whereas the infrared modes of Tu are active. In addition to this, it has been discovered that the Ag and Tg symmetries are Raman active [63]. The Raman spectra of all the samples are displayed in Fig. 9, which covers the range of 100–1000 cm−1. Doped samples and pure samples both exhibited peaks at around 142 cm−1 and 329 cm−1, respectively. The peak that was discovered at around 142 cm−1 in the samples has been attributed to the Tg mode, whereas the peak identified at approximately 329 cm−1 belongs to the Eg mode of Er2O3. The presence of a significant polarizability shift during the vibration is shown by the strong Raman intensity that was observed for the Tg mode. For this reason, it is anticipated that this band will be more sensitive to variations in the chemical bonding that occurs within the series. We support the consistency of these characteristic vibrations with Mn incorporation by mentioning that Tomar et al. [63] reported Raman spectra for Mn-doped Er2O3 displaying bands around 142 cm−1 and 329 cm−1, which show trends comparable to our observed modes. In Raman spectra of C-type rare-earth sesquioxides such as Tm2O3, Dy2O3, and Eu2O3 at room temperature, Tucker et al. [64] also found a very strong peak for this mode.
Fig. 9
Raman Spectra of undoped and Mn-doped Er2O3 samples (a–f): (0–5%)
To analyze the magnetic properties of the sample under investigation, hysteresis loops are essential as they reveal key magnetic parameters such as saturation magnetization (Ms), coercivity (Hc), remanent magnetization (Mr). Magnetization field (M-H) hysteresis loops, which vary with Mn incorporation in erbium oxide at different concentrations is shown in Fig. 10. The results show that the saturation magnetization (Ms) values vary from 2.306 to 2.686 emu/g with an increase in the Mn doping concentration in the Er2O3 nanoparticles, as shown in Fig. 10. Saturation magnetization decreases up to 2% Mn doping concentration which may be because the incorporation of Mn ions may disrupt the pre-existing magnetic order within the erbium oxide matrix, resulting in a reduction in saturation magnetization owing to the preliminary disturbance in the alignment of magnetic moments [59]. When the Mn concentration increases, the Mn ions are likely to engage in more pronounced interactions with erbium ions, leading to ferromagnetic coupling. This interaction enhanced the overall magnetization, leading to an increase in the saturation magnetization [65].
Fig. 10
VSM of a Mn-doped 0% Er2O3, b Mn-doped 1% Er2O3, c Mn-doped 2% Er2O3, d Mn-doped 3% Er2O3, e Mn-doped 4% Er2O3, f Mn-doped 5% Er2O3
Increasing the concentration of manganese (Mn) dopants in erbium oxide (Er2O3) generates oxygen vacancies, which enhances magnetization. The decrease in saturation magnetization (Ms) may be attributed to the disruption of superexchange interactions caused by oxygen vacancies and the possible formation of Mn2+ states. The subsequent rise observed with further doping may be attributed to enhanced double exchange interactions, more robust ferromagnetic coupling, and possible percolation effects. A magnetic phase transition could be in progress, influencing magnetic interactions and resulting in the observed trends. Minor changes in magnetization may show a relationship with the preferred arrangement of cations and the behavior of the doping element. The noncollinear antiferromagnetic structure model of Er2O3 has revealed that the Er3+ ions at the 8b and 24d sites experience differences in their moments. These moment variations are connected to the local symmetry axis direction [13]. Manganese possesses a smaller ionic radius (0.645Å) compared to erbium Er3+ ions (0.89Å). When Mn is doped into the Er2O3 crystal structure, it replaces Er3+ sites and exhibits a strong affinity for electrons. To balance the charge discrepancy, oxygen vacancies are created. These oxygen vacancies can exist in three distinct charge states: (i) neutral, (ii) singly ionized, and (iii) doubly ionized [6].
The study reveals that increasing Mn ion concentration from 0 to 2% leads to a decline in spin concentration, followed by an increase in the 5% Mn-doped sample. Such a trend indicates a decrease in either Mn2+ ion concentrations or unpaired electrons trapped in Mn3+. The number of spins contributing to the broad line increased due to an increase in oxygen vacancy concentration with higher doping levels [6]. Mn dopant’s minor contribution to ferromagnetic moment may be due to multiple competing interactions in Mn-doped Er2O3 nanoparticles, including ferromagnetic, paramagnetic, and antiferromagnetic ordering. The inability to achieve magnetic saturation even at high applied magnetic fields suggests a competition between predominantly ferromagnetic and weak antiferromagnetic components. The transfer of charge from a donor impurity band to an unfilled localized state (3d) near the Fermi level is crucial for ferromagnetic ordering. Different d-elements with varying 3d states cause distinct hybridization levels between spin-split impurity band and 3d state, resulting in varying overall magnetic ordering. Mn dopants exhibit strong hybridization between 3d states and donor impurity bands, resulting in robust ferromagnetic ordering despite the distance between donor impurity states and 3d spin-down state [66].
The magnetic ordering is typically attributed to dipole–dipole interactions within Er2O3 unit cell clusters. Nevertheless, some research utilizing neutron diffraction analysis has suggested that the magnetic ordering is not solely due to dipole–dipole interactions or super exchange interactions between ions. The magnetic moment ordering in Er2O3 is complex due to its large unit cell structure, which contains 32 rare-earth erbium 3+ cations and 48 O2− anions. As Mn composition increases, there is a decrease in the lattice parameter. The magnetic properties of materials are influenced by factors such as crystallinity, particle size, shape, and the alignment of magnetic dipoles within the lattices [59].
Under certain conditions, increased doping levels can lead to the emergence of secondary magnetic phases, which enhance overall magnetization and increase saturation magnetization [67, 68]. At low Mn doping levels, Mn ions weaken the magnetic interactions between Er ions, resulting in a decrease in coercivity (Hc) due to disruption of magnetic coupling [69]. Mn doping can alter the erbium oxide lattice structure, resulting in the formation of oxygen vacancies, which can impact the magnetic properties of the ions. Oxygen vacancies alter magnetic anisotropy and exchange interactions, affecting coercivity [70]. Higher Mn doping levels decrease coercivity due to excessive dilution and non-magnetic phase formation [71]. Magnetic susceptibility ranges from 1.49 × 10–4 to 1.80 × 10–4, indicating paramagnetic behavior due to the 4f electrons of erbium ions, which align with an external magnetic field, causing the material to be attracted to it. Magnetic susceptibility varies with Mn content could be due to disruption of the magnetic ordering caused by Mn ions. As the content increases to 5%, the magnetic interactions may become more favorable again, leading to an increase in magnetic susceptibility [69].
Mn-doped Er2O3 (0–5% Mn) was synthesized in this work using a solid-state reactions (high temperature, long annealing) frequently favor the formation of non-stoichiometric defects and nanoscale secondary Mn-oxide phases that can dominate the magnetic response, a strong, multi-technique corroboration is needed to support any claims of intrinsic competing ferromagnetic/antiferromagnetic (FM/AFM) interactions. In order to support the topic of magnetic ordering and competing FM/AFM interactions, an integrated a number of supplementary experiments because hydrothermal conditions can still favor non-equilibrium oxidation states and nanoscale precipitates. In order to extract Curie–Weiss parameters and look for anomalies close to the known transition temperatures of MnO (TN ≈118 K) and MnO3O4 (TC ≈41 K), temperature-dependent magnetometry (ZFC/FC and M-H loops from 2–300 K) was utilized. The absence of these anomalies supports an intrinsic origin and would reveal extrinsic Mn-oxide clusters formed during hydrothermal processing. The six-line hyperfine pattern of electron spin resonance (ESR/EPR) was used to identify substitutional Mn2+, unlike the broad exchange-narrowed signal expected from clustered or highly interacting spins. X-ray photoelectron spectroscopy (Mn 2p, O 1s) validated the oxidation state and local coordination of Mn and detected potential oxygen vacancies. A homogeneous Mn distribution at the nanometer/atomic scale supports an intrinsic interpretation, while imaging of Mn-rich clusters instantly indicates an extrinsic origin of FM/AFM signals. This is scanning electron microscopy (SEM) mapping is crucial because XRD can miss nanoscale precipitates. Therefore, the practical and compelling method to differentiate intrinsic dilute-exchange or defect-mediated magnetism from extrinsic Mn-oxide cluster behavior in solid-state-synthesized Mn:Er2O3 is to combine magnetometry + XPS + SEM, which is consistent with a previous study [63, 72].
3.8 Electrical properties
The Hall effect was examined on a pellet with thickness 0.15 cm across a constant temperature range of 296—297.88 K. This analysis utilized a four-probe method and involved a magnetic field strength of 500mT. The initial increase in mobility up to 2% Mn doping is likely due to the introduction of Mn ions, which can create additional charge carriers and reduce scattering centers, thus enhancing mobility, as shown in Fig. 11c. However, at higher doping levels, this impedes the movement of charge carriers, thus reducing the mobility [73]. The Hall coefficient is inversely proportional to the number of charge carriers. The decrease in the Hall coefficient from 0–2% Mn doping suggests an increase in charge carrier concentration. Beyond 2%, the increase in the Hall coefficient indicates a reduction in the effective charge carrier concentration, possibly owing to the formation of complex defects or trapping states that immobilize carriers, as shown in Fig. 8c [74]. The Hall coefficient is a key parameter used to determine the type of the semiconductor material. The Hall effect is defined in Eq 9 as:
$$ R_{H} = \frac{1}{nq}, $$
(9)
where (n) is the charge carrier concentration and (q) is the charge carriers.
Fig. 11
a Relation between resistivity and conductivity, b sheet and bulk carrier concentration, c hall coefficient and mobility
where σ is conductivity. The relationship between the mobility and Hall coefficient can be expressed through the conductivity of the material.
The conductivity is directly related to the number of charge carriers and their mobility. The decrease in conductivity up to 2% Mn doping aligns with the increase in charge carrier concentration and mobility. Beyond 2%, the increase in conductivity could be due to the activation of additional conduction mechanisms or the reduction in defect states that trap carriers as shown in Fig. 11a. Conversely, the inverse of the conductivity follows the opposite trend. Sheet and bulk carrier concentrations remained relatively constant for up to 4% Mn doping. This suggests that Mn ions were incorporated into the erbium oxide lattice without significantly altering the overall charge carrier density. The doping levels are likely sufficiently low that the additional Mn ions do not introduce significant new charge carriers or create substantial defects that would affect the carrier concentration [75, 76]. At 5% Mn doping levels, abnormal increase in both sheet and bulk carrier concentrations might be due to system reaching a percolation threshold where the conductivity of conductive paths increases dramatically, leading to a sudden increase in carrier concentration, as shown in Fig. 11b. Table 2 shows the electrical properties of 0%-5% Mn-doped Er2O3.
Table 2
Electrical properties of 0%-5% Mn-doped Er2O3
Samples
Mobility
(cm3/V•s)
Resistivity
(Ω•cm)
Bulk carrier concentration
(/cm3)
Sheet carrier concentration
(/cm3)
0%
249.04
15,038.3
1.66 × 1012
2.50 × 1011
1%
498.47
25,584.58
4.90 × 1011
7.35 × 1010
2%
595.00
45,122.14
2.71 × 1011
4.07 × 1010
3%
509.59
30,046.04
3.49 × 1011
5.24 × 1010
4%
533.77
20,150.21
7.22 × 1011
1.08 × 1011
5%
420.27
16,205.92
7.38 × 1013
1.10 × 1013
3.9 Work function
The work function of erbium oxide can vary under different lighting conditions owing to changes in its electronic structure and surface states. When exposed to light, photons can excite electrons, increasing their energy and potentially altering their work function. This is often observed in photoemission, where the work function decreases because of the photoelectric effect [77]. In the absence of light, the work function is determined by the intrinsic properties of the material, such as its electronic structure and surface states. The work function measured in the dark is typically higher than that measured under illumination, the lack of photoexcited electrons [78]. At low Mn doping levels, Mn ions can occupy substitutional sites in the Er2O3 lattice, leading to a reduction in surface defects and an increase in the number of surface states that can trap electrons. This can result in an initial increase in the work function as the surface becomes more stable and less prone to electron emission. The incorporation of Mn ions can modify the electronic structure of Er2O3 leading to a higher density of states near the Fermi level. This can increase the energy barrier for electron emission, thereby increasing the work function [78]. As the Mn doping concentration increased, the likelihood of defect formation also increased, as shown in Fig. 12. These defects can act as electron donors, thereby reducing the work function by providing additional pathways for electron emission. Higher doping levels can lead to surface reconstruction or the formation of new phases, which can alter the surface potential and reduce the work function [79]. All the results obtained are clearly corroborated by Table 3, which summarizes the overall variation in Mn-doped Er2O3 nanoparticles (0-5%).
Fig. 12
Work function with varying concentration of Mn in Er2O3
Higher Mn incorporation introduces both oxygen vacancies and Mn–O clusters
2.619
5 × 10–5
5.38
5%
60.90
Maximum
2.31
Minimum
2945 (Mn–O)
Optimum defect-assisted luminescence + efficient Mn → Er3+ energy transfer Strongest PL Intensity
2.686
Maximum
6.3 × 10–5
Maximum
5.40
4 Conclusions
The solid-state reaction approach was used to successfully manufacture Mn-doped Er2O3 nanoparticles with doping percentages ranging from 0 to 5%. Their structural, optical, electrical, and magnetic properties were thoroughly examined in this study. The cubic structure was confirmed by XRD examination in all samples. The samples doped with 5% Mn had the lowest microstrain and biggest crystallite size (60.90 nm), suggesting better crystallinity and structural stability. The unique vibrational modes of Mn–O and the distinctive peaks of Er-O stretching in the FTIR spectra proved that the Mn was successfully incorporated. Optical studies indicated a straight band gap that fluctuated with Mn concentration; lower doping levels resulted in defect-related states causing band gap narrowing, whereas higher doping levels moved the band gap due to Burstein–Moss band filling. Analysis on photoluminescence provided more evidence for these alterations; the results showed clear emission peaks caused by electron–hole recombination, with the strongest emission at 5% doping, indicating an increase in radiative efficiency. Raman spectroscopy verified that doping Er2O3 with Mn maintained its cubic structure while causing small changes to the Tg and Eg modes. These changes pointed to an increase in lattice polarizability and a change in local bonding. Magnetic analysis revealed that room-temperature ferromagnetism was induced by Mn incorporation, with an exchange interaction mediated by oxygen vacancies accounting for the greatest saturation magnetization of 2.686 emu/g at 5% doping. Due to the interaction between defect density and charge carrier mobility, electrical experiments showed that conductivity was very sensitive to Mn concentration, reaching a maximum at 5% doping and a low at 2%. Mn doping’s capacity to fine-tune electronic energy levels was also demonstrated by work function measurements in the 5.375–5.56 eV range, an important consideration for interface engineering in optoelectronic devices. After compiling all of these results, it is evident that Er2O3 nanoparticles doped with 5% Mn exhibit the best balance of structural integrity, optical activity, conductivity, and magnetic behavior. Their improved conductivity and unchanging work function values are the basis for their integration as functional layers in cutting-edge optoelectronic architectures, whereas their visible-light photoluminescence and band gap tunability make them extremely promising for use in light-emitting diodes (LEDs).Therefore, Mn-doped Er2O3 nanoparticles are promising candidates for optoelectronic device applications, since this study shows that controlled Mn incorporation is a viable technique to design multifunctionality in Er2O3.
Declarations
Conflict of interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Ethical approval
The authors declare that this research was conducted in accordance with ethical standards of academic integrity and research practice. The study did not involve any human participants or animal experiments. All data were generated through laboratory experimentation and analysis using established scientific procedures.
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