Crystal structure and spectroscopic properties of garnet-type Li7La3Hf2O12:Eu3+

Abstract

A promising series of phosphors based on Li7La3−xEuxHf2O12 (x = 0.05–0.20) has been prepared using a conventional solid state reaction. Rietveld refinement of room temperature powder X-ray diffraction patterns shows that the Li7La3−xEuxHf2O12 (x = 0.00–0.20) solid solution crystallizes in the tetragonal space group I41/acd, Z = 8. The trivalent europium ions occupy two crystallographically nonequivalent sites (8b) and (16e) with the D′2 and C2 symmetry, respectively. Raman spectroscopy corroborates the X-ray diffraction results and confirms the crystal structure features of tetragonal Li7La3Hf2O12 with the maximum phonon energy of 650 cm−1. The phosphors exhibit reddish orange emission under excitation at 282 nm. Calculation of the Ω2 and Ω4 Judd–Ofelt intensity parameters and quantum efficiencies from the recorded emission spectra allows a more extensive study of the luminescence properties of Eu3+-doped Li7La3Hf2O12. The maximum light emission is revealed at the activator content of x = 0.15 in Li7La3−xEuxHf2O12. CIE chromaticity coordinates of Li7La2.85Eu0.15Hf2O12 are x = 0.643 and y = 0.354.