Luminescence and microstructures of Eu3+-doped Ca9LiGd2/3(PO4)7

Abstract

A red-emitting phosphor, Eu³⁺-doped Ca₉LiGd_2/3(PO₄)₇, was synthesized by the conventional high-temperature solid-state reaction. X-ray powder diffraction (XRD) analyses confirmed the pure crystalline phase of Whitlockite-type structure. The excitation spectra of Eu³⁺ doped Ca₉LiGd_2/3(PO₄)₇ were measured in the VUV and UV region indicating an efficient energy transfer process from the host and Gd³⁺ to Eu³⁺ ions. Upon excitation with VUV and UV radiation, the phosphor showed strong red emission around 611 nm corresponding to the forced electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The VUV- and UV-excited luminescence spectra of Ca₉LiGd_2/3(PO₄)₇:Eu³⁺ together with the dependence of the integrated emission intensities on the doping levels were investigated. The Eu³⁺ ions were investigated by a tunable laser as an excitation source. The excitation spectra of ⁷F₀→ ⁵D₀ transitions suggest that there are two families of inequivalent sites for Eu³⁺ in this host. The concentration quenching and crystallographic site-occupancy of Eu³⁺ ions in Ca₉LiGd_2/3(PO₄)₇ host were discussed on the basis of the site selective excitation and emission spectra, the luminescence decay and its crystal structure.