Enhanced dual-wavelength sensitive upconversion luminescence of BiPO4:Yb3+/Er3+ phosphors by Sc3+ doping

doi:10.1016/j.mseb.2017.12.010

Materials Science and Engineering: B

Volume 229, March 2018, Pages 20-26

https://doi.org/10.1016/j.mseb.2017.12.010 Get rights and content

Highlights

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The BiPO₄:Yb/Er/Sc shows the dual-wavelength (980/1550 nm) sensitive UC emission.
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UC emission intensity was enhanced by doping Sc³⁺ ions under 980/1550 nm.
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The UC emission color were always green or yellow-green under 980/1550 nm.

Abstract

A series of BiPO₄:Yb³⁺/Er³⁺ samples with different concentrations of Sc³⁺ ions were prepared by two different methods: one is solvothermal synthesis process and subsequent calcination route, and the other is solid-state reaction method. On one hand, hexagonal and monoclinic phases of BiPO₄:Yb³⁺/Er³⁺ were successfully obtained by the above two synthesis methods, respectively, and the UC luminescence intensity depended a lot on the crystalline phases. On the other hand, the dual-wavelength sensitive UC emission properties of BiPO₄:Yb³⁺/Er³⁺/Sc³⁺ were firstly investigated. It was found the UC emission intensity was significantly enhanced by introducing appropriate Sc³⁺ ions to the system whether under excitation at 980 nm or 1550 nm. Moreover, the UC emission mechanisms under the excitation at 980 as well as 1550 nm were also proposed on the base of experimental results.

Graphical abstract

Dual-wavelength sensitive upconversion luminescence of the as-synthesized BiPO₄:Yb³⁺, Er³⁺ phosphors were significantly enhanced by Sc³⁺ ions doping under the excitation of 980 nm or 1550 nm.

Introduction

Lanthanide ions (Ln³⁺) doped inorganic materials showing upconversion (UC) emission properties have been attracted more and more attention due to their potential applications in some fields, such as laser lighting or displays [1], [2], [3], temperature sensors [4], [5], [6], biomedical imaging [7], [8], [9], photodynamic therapy [9], [10] and solar cells [11], [12], [13] etc. Recently, the rare-earth orthophosphates (REPO₄) as an important UC material attracted broad attention due to their low sintering temperature, chemical stability and environment friendly characteristics [14]. However, obtaining large quantities of rare-earth ions (REs), in a highly pure form, which is essential when REPO₄ is used as the host material, is much more costly. Considering the main group elements like Sb and Bi are relatively much cheaper, the similar ionic radii of Bi³⁺ and RE³⁺, and the fact that BiPO₄ is isostructural to REPO₄ [15], BiPO₄ was chosen as the investigated system in this paper. Also, it should be noted that Ln³⁺ co-doped BiPO₄ with low dimensional structure shows promising temperature transformation. It reported that there would be some changes in the position of the nearest oxygen of the Bi³⁺ ion towards LaPO₄, if Bi³⁺ ions incorporate in LaPO₄ host materials. Therefore, it is reasonable to believe that the oxygen coordination of Ln³⁺ is disordered in the BiPO₄ crystal structure [16]. As a result, it can be expected that the doping or substituting foreign ions into the lattice of parent compounds would introduce local distortion, and these local distortions could pin the structure of parent compounds. For the host of UC materials, it is well-known that BiPO₄ mainly exists in two crystalline forms namely the hexagonal and monoclinic. The essential difference in the hexagonal and monoclinic form is the coordination number around Bi³⁺. In the case of hexagonal BiPO₄, Bi³⁺ is surrounded by eight oxygen atoms, whereas in monoclinic BiPO₄, Bi³⁺ has a coordination number of nine, similar to the monazite structure of lanthanide phosphate [17]. Until now, only a few works about UC luminescence properties of BiPO₄:RE³⁺ materials under excitation at 980 nm were reported. In 2013, Zhang’ group [18] synthesized uniform rice-shaped BiPO₄ UC submicron particles and obtained multicolor/bright white UC emissions by means of precisely adjusting the concentration of the dopant RE³⁺ (RE = Yb, Er, Tm and Ho) ions. In 2015, Zhang’ group [19] studied that the phase of BiPO₄:Er³⁺/Yb³⁺ phosphors changed from hexagon to monocline and the morphology changed from nanorods through nanorugbies to microoctahedra with the extension of aging time.

Actually, besides being excited under 980 nm, the Er³⁺ ion can also be excited under 1550 nm, because the metastable ⁴I_13/2 level of Er³⁺ has a long lifetime [20], [21], [22], [23], [24], [25]. Moreover, it is essential to study the excellent UC luminescence performance of Er³⁺ ions induced by excitation under 1550 nm in order to enlarge the solar spectrum response. By contrast, there are not any investigation about BiPO₄:RE³⁺ UC luminescence under excitation at 1550 nm. Meanwhile, the application of BiPO₄:Yb³⁺/Er³⁺ phosphors is still very much constrained due to their low UC intensity.

How to improve the UC luminescence intensity? Electronic transition probabilities and self-specific absorption of UC emission are two determinant factors of the UC luminescence intensity. In 2004, François Auzel [26] elaborated UC luminescence and anti-Stokes processes with f and d ions in solids. According to many previous reports, electronic transition probabilities are significantly affected by the local crystal field symmetry of RE ions. It will break the symmetry of the crystal field around the host lattice and RE ions’ surrounding environment by co-doping with foreign ions [27], [28], [29], [30], [31], [32], in order to enhance UC luminescence intensity. On account of these reasons, we consider that the co-doping one smaller trivalent ion (Sc³⁺) into BiPO₄:Yb³⁺/Er³⁺ phosphors would decrease the crystal field symmetry around Yb³⁺ and Er³⁺ ions, leading to enhancement of the UC luminescence intensity. In fact, Yu et al. [30] reported that the blue, green, red and UV UC emissions of hexagonal NaYF₄:Er³⁺/Yb³⁺ were obviously enhanced by doping with Sc³⁺. Yu’ group [31] presented a report on the synthesis of (Y_0.1Yb_0.05Er_0.005Sc_xAl)₂O₃. The asymmetry of Er³⁺ local surrounding has been improved, with the increasing of Sc³⁺ co-doping concentration. As a result, the UC luminescence intensity has been enhanced several times, and so on. While these studies are only limited to excitation at 980 nm.

Herein, considering the effects of excitation wavelength and structures on UC performance of BiPO₄ by different preparation methods have not been reported so far. In this work, dual-wavelength (980 and 1550 nm) sensitive UC luminescence of BiPO₄:Yb³⁺/Er³⁺/Sc³⁺ phosphors were prepared by solid-state route and solvothermal synthesis, respectively. The explanation for the power density dependence of the UC emission intensity is given. Additionally, the mechanism of the enhanced UC emission intensity of the as-synthesized BiPO₄:Yb³⁺,Er³⁺ with Sc³⁺ ions doped under the excitation of 980 nm or 1550 nm LD was also investigated, which will be a meaningful research work.

Section snippets

Materials

Bi(NO₃)₃⋅5H₂O (AR grade), Yb₂O₃ (99.99%), Er₂O₃ (99.99%), Sc₂O₃ (99.99%), NH₄H₂PO₄ (AR grade), NaH₂PO₄ (AR grade) and ethanol were purchased from Aladdin Chemical Reagent Factory (China). and were used as starting materials without further purification. Deionized water used as solvent throughout the experiment.

All the rare earth nitrate were obtained by dissolving the corresponding rare earth oxides in dilute HNO₃ under heating with agitation followed by evaporating the solvent.

Samples synthesized by a solid-reaction method

The rare earths

Structure and morphology of powders

The crystal phase of samples prepared by two different methods were investigated by XRD. As shown in Fig. 1a, if the samples were prepared by solid-state method, the XRD patterns were found to be in good agreement with monoclinic phase of pure BiPO₄ (JCPDS card No. 43-0637). By contrast, samples prepared by solvothermal method display different phases before and after calcining at 800 °C for 4 h. Before calcination (Fig. 1c), the patterns of the obtained samples match well with the standard

Conclusion

Monoclinic and hexagon phases of BiPO₄:15% Yb³⁺, 2% Er³⁺, x% Sc³⁺ (x = 0, 1, 3 and 5) samples were prepared via solid-state route and solvothermal synthesis, respectively. Firstly, it is interesting to find that the BiPO₄:15% Yb³⁺, 2% Er³⁺, x% Sc³⁺ (x = 0, 1, 3 and 5) samples with hexagon phase could not exhibit any UC emission, while these samples with monoclinic phase shows the strong dual-wavelength sensitive UC emission, depending a lot on the phase structure. Secondly, the dual-wavelength

Acknowledgements

The authors gratefully acknowledge the China Postdoctoral Science Foundation (2016M592308), Chinese Academy of Sciences (Grants XDA09030203).

References (38)

Y.Q. Qu et al.
Preparation and characterization of upconversion luminescent LaF₃:Yb³⁺, E^r3+/La_F3 core/shell nanocrystal
Appl. Surf. Sci.
(2011)
A.K. Soni et al.
Yb³⁺ sensitized Na₂Y₂B₂O₇:Er³⁺ phosphors in enhanced frequency upconversion, temperature sensing and field emission display
Mater. Res. Bull.
(2017)
J. de Wild et al.
Enhanced near-infrared response of a-Si: H solar cells with β-NaY_F4:Y^b3+ (18%), E^r3+ (2%) upconversion phosphors
Sol. Energy Mater. Sol. Cells
(2010)
Y.X. Liu et al.
Effects of aging time on phase, morphology, and luminescence by two-photon processes of BiPO₄:Er³⁺, Yb³⁺ in the solvothermal synthesis
Opt. Mater.
(2015)
H. Wang et al.
Upconversion luminescence of Y₂O₃:Yb, Er under 1.55 μm excitation
Ceram. Int.
(2015)
X.M. Yin et al.
High color purity red emission of Y₂Ti₂O₇:Yb³⁺, E^r3+ under 1550 and 980 nm excitation
J. Lumin.
(2017)
G.Y. Chen et al.
Enhanced multiphoton ultraviolet and blue upconversion emissions in Y₂O₃:Er³⁺ nanocrystals by codoping with Li⁺ ions
Solid State Commun.
(2008)
H.J. Liang et al.
Enhancement of upconversion luminescence of Y₂O₃:Er³⁺ nanocrystals by codoping Li⁺-Zn²⁺
J. Alloys Compd.
(2011)
H. Yu et al.
Inhibiting emission quenching in (Y_0.1Yb_0.05Er_0.005Al)₂O₃ by Sc³⁺ co- doping to enhance upconversion luminescence
J. Lumin.
(2013)
Z.P. Li et al.
Selective enhancement of green upconversion emissions of Er³⁺:Yb₃Al₅O₁₂ nanocrystals by high excited state energy transfer with Yb³⁺-Mn²⁺ dimer sensitizing
J. Lumin.
(2012)

Y.L. Ding et al.

Enhancement on concentration quenching threshold and upconversion luminescence of β-NaYF₄:Er³⁺/Yb³⁺ codoping with Li⁺ ions

J. Alloys Compd.

(2014)

H. Wang et al.

Upconversion emission colour modulation of Y₂O₂S:Yb, Er under 1.55 μm and 980 nm excitation

J. Alloys Compd.

(2014)

F. Wang et al.

Recent advances in the chemistry of lanthanide-doped upconversion nanocrystals

Chem. Soc. Rev.

(2009)

J. Zhou et al.

Upconversion luminescent materials: advances and applications

Chem. Rev.

(2015)

F. Vetrone et al.

Temperature sensing using fluorescent nanothermometers

ACS Nano

(2010)

W. Yu et al.

Temperature-dependent upconversion luminescence and dynamics of NaYF₄:Yb³⁺/Er³⁺ nanocrystals: influence of particle size and crystalline phase

Dalton Trans.

(2014)

G.C. Kagadis et al.

In vivo small animal imaging: current status and future prospects

Med. Phys.

(2010)

N. Lee et al.

Nano-sized CT contrast agents

Adv. Mater.

(2013)

H. Dong et al.

Lanthanide nanoparticles: from design toward bioimaging and therapy

Chem. Rev.

(2015)

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It is clearly found that the (200) diffraction peaks of HP Cr-doped BiPO4 samples exhibit a discernible shift to low angle (from 2θ = 29.561° to 29.502°) with the increase of Cr3+ content in the compounds, which should be attributed to the ionic radius of Cr3+ (0.615 Å; coordination number = 6) is much smaller than that of Bi3+ (1.17 Å; coordination number = 8) [12] and a relatively low amount of doping. In other words, the reason for (200) diffraction peaks shift is Cr3+ ions with smaller ion radii enter the interstitial sites, which leads to the expansion of interplanar distance and lattice [13]. Thus, the solid solution of Cr-doped BiPO4 was formed in the prepared pigments.
A series of new green Cr-doped BiPO₄ materials were synthesized by hydrothermal method and first used as solar heat-reflective pigments. XRD, FTIR, FE-SEM and HR-TEM analyses confirm that the phase structure was transformed from low-temperature monoclinic phase (LTMP) to hydrated hexagonal phase (HP), the particle size decreased and the morphology changed from irregular prism-shaped to rod-shaped, which all attributed to the incorporation of Cr³⁺ ions. Moreover, the valance of chromium ions was also confirmed by XPS. Color and ultraviolet-visible-near-infrared (UV–Vis–NIR) analysis indicate that different hues of green were obtained in these solid solutions and they possessed high NIR reflectance (>83%) and solar reflectance (>86%) in total NIR region. Meanwhile, the reason of decrease in NIR reflectance of doped samples was also analyzed, which mainly due to the decrease of free carrier concentration. TG-DTA and corrosion resistance tests prove that these pigments have excellent thermal and chemical stability. Compared with pure PMMA and the existing reports on pigmented PMMA, the NIR reflectance of PMMA pigmented with Cr-doped BiPO₄ pigments have been greatly improved and have good coloring performance. The NIR solar reflectance of PMMA colored with Bi_0.85Cr_0.15PO₄ in shortwave NIR region reaches up to 77.83%, an increase of nearly 52%. Heat aging test shows that Cr-doped BiPO₄ pigments significantly improve the aging resistance of PMMA. In conclusion, these pigments have potential to become plastic colorants to increase the NIR reflectance and aging resistance of plastics.
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Enhanced dual-wavelength sensitive upconversion luminescence of BiPO4:Yb3+/Er3+ phosphors by Sc3+ doping

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Samples synthesized by a solid-reaction method

Structure and morphology of powders

Conclusion

Acknowledgements

Appl. Surf. Sci.

Mater. Res. Bull.

Sol. Energy Mater. Sol. Cells

Opt. Mater.

Ceram. Int.

J. Lumin.

Solid State Commun.

J. Alloys Compd.

J. Lumin.

J. Lumin.

J. Alloys Compd.

J. Alloys Compd.

Recent advances in the chemistry of lanthanide-doped upconversion nanocrystals

Chem. Soc. Rev.

Upconversion luminescent materials: advances and applications

Chem. Rev.

Temperature sensing using fluorescent nanothermometers

ACS Nano

Temperature-dependent upconversion luminescence and dynamics of NaYF4:Yb3+/Er3+ nanocrystals: influence of particle size and crystalline phase

Dalton Trans.

In vivo small animal imaging: current status and future prospects

Med. Phys.

Nano-sized CT contrast agents

Adv. Mater.

Lanthanide nanoparticles: from design toward bioimaging and therapy

Chem. Rev.

Enhanced dual-wavelength sensitive upconversion luminescence of BiPO₄:Yb³⁺/Er³⁺ phosphors by Sc³⁺ doping

Temperature-dependent upconversion luminescence and dynamics of NaYF₄:Yb³⁺/Er³⁺ nanocrystals: influence of particle size and crystalline phase