Electronic and spectroscopic studies of rare earth doped yttrium strontium silicate fluorapatite compound

Abstract

This paper reports the luminescence studies and first principle calculations based on density functional theory (DFT) using B3LYP/def2-SVP hybrid GGA function of rare earth doped yttrium strontium silicate fluorapatite (Y6-xSr4(SiO4)6F2:xEr3+) compound synthesized by solution combustion method and characterized by XRD, SEM and Raman spectroscopy. Raman spectra of synthesized compound confirms the formation of symmetric and asymmetric bending and stretching Raman active modes within SiO4 tetrahedron. Photoluminescence spectroscopy of Y6-xSr4(SiO4)6F2:xEr3+ compounds show emission spectra at 522 nm with high lumen intensity attributing to 2H11/2 – 4I15/2 electric dipole transition in the green region under 260 nm UV excitation radiation. In the thermoluminescence analysis prepared compound shows the presence of six trap levels where difference between the shallowest and deepest trap was found to be 1.396 eV, as calculated by computerised glow curve deconvolution (CGCD). The computational crystal structure shows a good agreement with experimental structural (XRD) analysis which confirms the formation of hexagonal closed packed structure along with space group P63/m. Frontier molecular orbital calculations were done and the value of ΔE = 5.05243 eV and 1.60969 eV were calculated for Y6Sr4(SiO4)6F2 and Y5ErSr4(SiO4)6F2 compounds. The Mulliken population of Er – O is more than Y – O which shows that covalency of Y5ErSr4(SiO4)6F2 is more than covalency of Y6Sr4(SiO4)6F2 compound. The electronic band structure and total density of states of Er3+ ion substituted Y6-xSr4(SiO4)6F2 shows semiconducting behaviour of compounds.