Preparation and spectroscopic properties of rare-earth (RE) (RE = Sm, Eu, Tb, Dy, Tm)-activated K2LnZr(PO4)3 (Ln = Y, La, Gd and Lu) phosphate in vacuum ultraviolet region

Rare earth (RE = Sm, Eu, Tb, Dy and Tm)-activated K2LnZr(PO4)3 (Ln = Y, La, Gd and Lu) have been synthesized by solid-state reaction method, and their vacuum ultraviolet (VUV) excitation luminescent characteristics have been investigated. The band in the wavelength range of 130–157 nm and the other one range from 155 to 216 nm with the maximum at about 187 nm in the VUV excitation spectra of these compounds are attributed to the host lattice absorption and O–Zr charge transfer transition, respectively. The charge transfer bands (CTB) of O2−Sm3+, O2−Dy3+ and O2−Tm3+, in Sm3+, Dy3+ and Tm3+-activated samples, have not been obviously observed probably because the 2p electrons of oxygen are tightly bound to the zirconium ion in the host lattice. For Eu3+-activated samples, the relatively weak O2−Eu3+ CTB at about 220 nm is observed. And for Tb3+-activated samples, the bands at 223 and 258 nm are related to the 4f-5d spin-allowed and spin-forbidden transitions of Tb3+, respectively. It is observed that there is energy transfer between the host lattice and the luminescent activators (e.g. Eu3+, Tb3+). From the standpoint of luminescent efficiency, color purity and chemical stability, K2GdZr(PO4)3:Sm3+, Eu3+, Tb3+ are attractive candidates for novel yellow, red, green-emitting PDP phosphors.