Synthesis, Crystal Structure and Photoluminescence Properties of Eu²⁺-Activated RbCaGd(PO₄)₂ Phosphors

A series of novel double-phosphate compounds RbCaGd(PO₄)₂:Eu²⁺ were first synthesized by the Pechini-type sol–gel method, and their structure and luminescence properties were characterized in detail. The compound RbCa_0.97Gd(PO₄)₂:0.03Eu²⁺ crystallizes in the hexagonal system with space group P6₂22 and the parameters a = 7.006(49) Å, c = 6.358(80) Å, and V = 269.969 ų, Z = 1. Its crystal structure is similar to that of hexagonal LnPO₄, where the Rb atom occupies a large tunnel in the lattice and the Ln position is statistically occupied by both Gd and Ca (Eu) atoms. In addition, RbCaGd(PO₄)₂:Eu²⁺ produces an intense broadband emission from 400 to 600 nm with the CIE coordinates near (0.2089, 0.2674) and assembles a broad excitation spectrum from 250 to 425 nm. The concentration quenching, crystal field splitting, critical energy transfers distance and thermally stable luminescence properties of RbCaGd(PO₄)₂:Eu²⁺ phosphors are all discussed, which indicate that this material can be considered as a promising bluish green phosphor for application in white-light UV LEDs.