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