Effect of Mn doping on the structural and optical properties of SnO2 nanoparticles

doi:10.1016/j.jallcom.2012.01.072

Journal of Alloys and Compounds

Volume 523, 15 May 2012, Pages 83-87

https://doi.org/10.1016/j.jallcom.2012.01.072 Get rights and content

Abstract

Mn doped SnO₂ nanoparticles were synthesized by sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), UV-Visible absorption spectroscopy, photoluminescence (PL), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy measurements. XRD analysis revealed the formation of single phase rutile type tetragonal structure of all samples which was further supported by Raman studies and FTIR measurements. Crystallite size was observed to vary from 16.2 nm to 7.1 nm as the Mn content increased from 0% to 15%, suggesting the prevention of crystal growth with Mn doping. It was evident from the absorption spectra that the absorbance tends to increase with the increase in dopant concentration. Optical band gap was calculated using Tauc relation and found to increase with the increase in Mn content confirming the size reduction as a result of Mn doping. Raman spectroscopy measurement depicted the broadening of most intense Raman peak observed at 630 cm⁻¹ with Mn doping, indicating that the Mn ions are substituted at the Sn sites in SnO₂ matrix. Room temperature PL spectra revealed that the intensity of luminescent emission tends to increase with the increase in Mn concentration.

Highlights

► A significant decrease in particle size has been observed with the increase in manganese concentration, without affecting the rutile structure of SnO₂. ► Reduction in particle size is confirmed by both XRD and TEM. ► Photoluminescence spectra show that luminescence increases with the increase in manganese concentration.

Introduction

Synthesis and characterization of nanoscale materials is gaining popularity among the scientific community for fundamental as well as applied research point of view because many material properties change drastically as particle size reaches the nanometer range. The optical properties of nanocrystalline semiconductors have been studied extensively in recent years for translating their enhanced properties into practical applications. As the size of the material becomes smaller, the band gap becomes larger thereby changing the optical and electrical properties of the material and making the material suitable for new applications and devices. Tin oxide (SnO₂) is one of the most important n-type wide-band gap (3.6 eV) semiconductor. Its unique conductance has been utilized for various applications like gas sensors [1], microelectronics [2], solar cells [3] and photoelectrochemistry [4]. The compound has also been examined as possible electrode material for lithium cells [5] and photocatalysts [6]. As an n-type semiconductor, SnO₂ shows very high sensitivity towards reducing gases such as H₂, CO, hydrocarbon, and alcohol. It combines the low electrical resistance with high transparency in visible range and high reflectivity in infra-red region. This property of SnO₂ makes it a prominent candidate for optoelectronic applications. The optoelectronic properties such as photoluminescence and optical band gap of SnO₂ can also be improved by impurity doping. Many results have shown that several dopants (Co, Fe, Cu) can lead to an increase of surface area of SnO₂ by reducing the grain size and crystallanity [7], [8], [9]. Several authors have studied the effect of transition metal ions (Fe, Co, Ni, Cu) on the optical and electrical properties of SnO₂ nanoparticles [7], [8], [9], [10], [11]. Azam et al. studied the electrical properties of Ni-doped SnO₂ nanoparticles and reported that the ac conductivity increases with Ni content [10]. Ahmed et al. discussed fluorescence properties of Ni-doped SnO₂ nanoparticles and reported that the visible emission increases as the dopant concentration increases [11]. Fang et al. reported the luminescence properties of Co-doped SnO₂ nanoparticles; they have shown that the blue emission increases with the increase in Co-doping [12].

Various approaches have been adopted for the synthesis of SnO₂ nanoparticles including the hydrothermal method [13], [14], solvothermal method [15], gel-combustion method [16] and sol–gel method [17]. Amongst all, the sol–gel method for the synthesis of SnO₂ nanoparticles has a number of advantages including low temperature processing and molecular level homogeneity.

This paper reports the effect of Mn doping on the structural and optical properties of SnO₂ nanoparticles prepared by sol–gel method. Analyses were carried out using techniques like XRD, TEM, EDAX, FTIR, Raman, UV-Visible and PL spectroscopy.

Section snippets

Experimental

Details of synthesis of pure and Mn doped SnO₂ nanoparticles are reported in our earlier communication [18]. Analytical grade SnCl₄·5H₂O and MnCl₂·4H₂O were used as starting materials for the synthesis of Sn_1−xMn_xO₂ series. In a typical synthesis procedure, citric acid was added to 100 ml of distilled water with magnetic stirring, until pH becomes 1.5. Required amounts of SnCl₄·5H₂O and (x = 0, 0.03, 0.05, 0.07, 0.09 and 0.15) MnCl₂·4H₂O were added to the solution and dissolved completely. 10 ml of

X-ray diffraction analysis

The characteristic XRD spectra of the pure and Mn-doped SnO₂ nanoparticles annealed at 400 °C are depicted in Fig. 1. The peak positions of each sample exhibit the rutile structure of SnO₂ which were very well matched with the standard ICDD card No. 77-0452 without any characteristic peaks of impurities, confirming the single phase formation of the material. Table 1 shows the variation of crystallite size, lattice parameter and cell volume of different samples. It can be observed from Table 1

Conclusions

In summary, Mn-doped SnO₂ nanoparticles were successfully synthesized using sol–gel method. The XRD spectra exhibit the rutile type tetragonal structure of all the samples and no impurity phase was observed in XRD. It was found that with the increase in manganese concentration there was a decrease in the crystallanity, crystallite size and lattice constant. The three fundamental Raman modes of SnO₂ nanoparticles also confirm the rutile symmetry of all the samples. Optical band gap was found to

Acknowledgement

Mr. Arham S. Ahmed is thankful to CSIR, New Delhi for providing financial support in the form of SRF.

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Effect of Mn doping on the structural and optical properties of SnO2 nanoparticles

Abstract

Highlights

Introduction

Section snippets

Experimental

X-ray diffraction analysis

Conclusions

Acknowledgement

Mater. Chem. Phys.

Thin Solid Films

Sol. Energy Mater. Sol. Cells

J. Photochem. Photobiol. A Chem.

Mater. Chem. Phys.

Thin Solid Films

J. Alloys Compd.

J. Lumin.

Mater. Lett.

Colloids Surfaces A

Nanostruct. Mater.

Nanostruct. Mater.

J. Alloys Compd.

Mater. Lett.

Effect of Mn doping on the structural and optical properties of SnO₂ nanoparticles