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

A red-emitting phosphor, Eu3+-doped Ca9LiGd2/3(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 Ca9LiGd2/3(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 D-5(0)-> F-7(2) transition of Eu3+ ions. The VUV- and UV-excited luminescence spectra of Ca9LiGd2/3(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 F-7(0)-> D-5(0) 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 Ca9LiGd2/3(PO4)(7) host were discussed on the basis of the site selective excitation and emission spectra, the luminescence decay and its crystal structure.