Electronic and optical studies of Eu3+ doped Ca6-xNa2Y2(SiO4)6F2 fluorapatite ceramic synthesized by solution combustion method

Abstract

This paper reports, the electronic and optical properties of Ca6-xNa2Y2(SiO4)6F2:xEu3+ (x = 0–0.05 mol%) fluorapatite ceramic prepared by solution combustion method. The electronic properties such as energy band gap, total density of states, partial density of states, frontier molecular orbitals and mulliken population analysis were investigated with B3LYP hybrid GGA function by density functional theory (DFT). The lattice parameters value of Ca6Na2Y2(SiO4)6F2 fluorapatite ceramic calculated by DFT shows a good agreement with experimental crystallographic (XRD) analysis. The least square approach was used for computation of crystallographic parameters through Rietveld refinement analysis of XRD patterns. Fourier transform infrared (FTIR) spectra show four different symmetric stretching and bending modes due to the presence of (PO4), (CO2) and (OH) groups in Ca6-xNa2Y2(SiO4)6F2:xEu3+ fluorapatite ceramic. The band gap value calculated by DFT was 5eV whereas calculated by UV–visible spectroscopy was 4.1 eV, which shows the insulating behaviour of Ca6Na2Y2(SiO4)6F2 ceramic. From frontier molecular orbital calculations the energy band gap between HOMO and LUMO states was found to be 5.194 eV. Mulliken population analysis shows that Ca1, Na1, Si1 and F1 are main electron donors whereas Y1 and O1 are main electron acceptor atoms in Ca6Na2Y2(SiO4)6F2 ceramic. It also confirms that Y bonds are more covalent in nature than Na and Ca bonds. Photoluminescence (PL) spectroscopy of Ca6-xNa2Y2(SiO4)6F2:xEu3+fluorapatite ceramic shows three intense peaks at 600 nm, 623 nm and 698 nm perceiving 5D0 – 7F1, 5D0 – 7F2 and 5D0 – 7F4 transitions in orange and red regions under 250 nm UV excitation. The CIE chromaticity diagram shows cool emission in red and orange region with an application in optical and electronic devices.