Electronic structure and optical properties of TbPO4: Experiment and density functional theory calculations

doi:10.1016/j.optmat.2015.06.025

Optical Materials

Volume 47, September 2015, Pages 484-489

https://doi.org/10.1016/j.optmat.2015.06.025 Get rights and content

Highlights

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Single crystals of TbPO₄ are synthesized.
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The obtained product is characterized by different techniques.
•
Electronic structure, luminescence and optical properties are investigated.
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The DFT method is based on a combination of the GGA and the LDA+U approaches.
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The calculated values are compared to the phosphate experimental data.

Abstract

Single crystals of TbPO₄ were grown by high temperature solid-state reaction and identified by means of X-ray diffraction, infrared and Raman spectroscopies analysis. The electronic properties of TbPO₄ such as the energy band structures, density of states were carried out using density functional theory (DFT). We have employed the LDA+U functional to treat the exchange correlation potential by solving Kohn–Sham equation. The calculated total and partial density of states indicate that the top of valance band is mainly built upon O-2p states and the bottom of the conduction band mostly originates from Tb-5d states. The population analysis indicates that the P–O bond was mainly covalent and Tb–O bond was mainly ionic. The emission spectrum, color coordinates and decay curve were employed to reveal the luminescence properties of TbPO₄. Moreover, the optical properties including the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum are investigated and analyzed. The results are discussed and compared with the available experimental data.

Graphical abstract

Single crystals of TbPO₄ are synthesized by high temperature solid-state reaction method and characterized by different techniques. TbPO₄ crystallizes in the tetragonal system (I4₁/amd). A combination of the GGA and the LDA+U approaches is used to estimate the electronic and optical properties of TbPO₄. The lifetime and chromatic coordinates of the green emission of TbPO₄ are investigated.

Introduction

In recent years, rare-earth monophosphates have attracted attention due to their potential applications in different fields of optoelectronics due to their special optical, electronic, and chemical properties resulting from the 4f electron configuration [1], [2], [3], [4], [5], [6]. These properties have caused increased interest in their use in a wide range of applications such as phosphors, solid state displays, high-temperature protonic conductors, catalysts, fuel cells and heat-resistant materials [7], [8], [9], [10]. Today, theoretical studies have become effective methods to study the electronic structure, optical properties, crystallographic evolution, morphology, and the reaction mechanism [11], [12], [13], [14], [15]. Recently, density functional calculations are used to investigate the enthalpies of formation of rare-earth monophosphates and to make a comparative analysis of their experimental and theoretical vibrational dynamics [16], [17]. To our knowledge, there are not any theoretical results on the electronic and optical properties of TbPO₄, including the dielectric function, absorption coefficient, reflectivity, and energy-loss function. In order to fully take advantage of the properties of TbPO₄ for eventual technological applications, a theoretical investigation whose predictive capability and understanding can guide further experiments, is necessary. Therefore, we think that it is worthwhile to perform first-principles calculations for the electronic and optical properties of TbPO₄.

In this work we will present synthesis, and optical measurements for TbPO₄. At the same time, we also make the calculations of crystal energy band structure, densities of states and optical responses are performed with the Density Functional Theory plus U (DFT+U) method.

Section snippets

Synthesis

Single crystals of TbPO₄ were synthesized by high temperature solution reaction. Analytical reagents Tb₂O₃ and NH₄H₂PO₄ at the molar ratio of Tb/P = 1/20 were finely ground in an agate mortar to ensure the best homogeneity and reactivity. The mixture was placed in a platinum crucible and heated at 573 K for 4 h in order to decompose NH₄H₂PO₄. Afterwards, the solid mixture was reground and heated to 1273 K for 24 h. Finally, the temperature was cooled to 1073 K at a rate of 2 K/h and air-quenched to

Characterization

Powder XRD experimental and calculated patterns of TbPO₄ are shown in Fig. 1, which demonstrates that the experimental XRD pattern is in agreement with the corresponding calculated. The picks in the XRD pattern are indexed to the tetragonal system with the space group I4₁/amd (ICDD–PDF 076-1531). The peak located at 30° was identified as Tb₂O₃ phase (JCPDS–PDF 76-0156) in its cubic crystalline system. The refined unit cell parameters by the TREOR program correspond to TbPO₄: a = b = 6.9414 (2) Å; c =

Conclusions

In this work, single crystals of TbPO₄ has been synthesized and characterized by powder X-ray diffraction and spectral measurements. It crystallized in the tetragonal system with the space group I4₁/amd. We have performed DFT pseudopotential approach with adding a Hubbard parameter U for considering the strong Coulomb correlation between localized Tb 4f electrons to investigate the electronic and optical properties of TbPO₄. The obtained results show that TbPO₄ has an insulator character with

Acknowledgements

This work was supported by the Ministry of Higher Education, Scientific Research (MHESR) – Tunisia.

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Electronic structure and optical properties of TbPO4: Experiment and density functional theory calculations

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis

Characterization

Conclusions

Acknowledgements

J. Lumin.

J. Radiat. Meas.

Mater. Chem. Phys.

Mater. Chem. Phys.

J. Alloys Compd.

J. Lumin.

Res. Chem. Intermed.

Spectrochim. Acta

Spectrochim. Acta

J. Rare Earth

Opt. Mater.

Solid State Sci.

J. Alloys Compd.

J. Lumin.

Thin Solid Films

Handbook of Laser Wavelengths

Tunisian Patent SN

Cryst. Eng. Commun.

J. Mater. Chem.

J. Phys. Chem. C

J. Phys. Chem. B

Acta Mater.

J. Phys. Chem. C

Am. Mineral.

Phys. Rev. B

Am. Mineral.

J. Phys. Condens. Mater.

Electronic structure and optical properties of TbPO₄: Experiment and density functional theory calculations