Judd–Ofelt analysis and photoluminescence properties of europium-activated Y8−xSr2(SiO4)6O2 oxyapatite phosphors

In the present study, the solution combustion reaction method was employed to synthesize the Y8−xSr2(SiO4)6O2:xEu (YSSO:Eu) oxyapatite phosphors where x = 0.10, 0.15, 0.20, 0.25, and 0.30 mol%. The crystal phase study was done using X-Ray Diffraction analysis which confirmed apatite phase formation with hexagonal crystal symmetry and the average crystallite size was found to be 9.35 nm. The FTIR (Fourier Transform Infrared Spectroscopy) spectra were well evident for the bond formations and the presence of functional groups in the prepared sample. Using UV–Visible spectroscopy, band gap values were calculated, and with increasing doping concentrations, the band gap values decreased. The photoluminescence spectral analysis showed peaks at 582 nm, 587 nm, 593 nm, 611 nm, 624 nm, and 675 nm due to transitions of Eu3+ ions from 5D0 (excited state) to 7Fj (j = 0, 1, 2, 3) (ground state), respectively. The Y8−xSr2(SiO4)6O2:0.25Eu oxyapatite phosphor showed the highest intensity peak. The critical distance of energy transfer was calculated to be 4.17 Å implying exchange interaction in the sample. The Judd–Ofelt analysis of synthesized phosphors gave different optical europium transition parameters. The asymmetric environment around the ligand was indicated by the trend, Ω2 > Ω4 followed by J–O parameters. The values of fluorescence branching ratios were found to be more than 0.5 for all doping concentration and the highest calculated lifetime was found to be 9.787 ms for Y8−xSr2(SiO4)6O2:xEu (x = 0.25 mol%) phosphor.