Effects of crystal structure on the luminescence properties and energy transfer between Gd3+ and Ce3+ ions in MGd(PO3)4:Ce3+ (M = Li, Na, K, Cs)

Abstract

Cerium-activated polyphosphates MGd(PO₃)₄ (M = Li, Na, K, Cs), were synthesized by a solid-state reaction technique at high temperature. The ultraviolet (UV) and vacuum ultraviolet (VUV) luminescence spectra of this series of samples were determined at room temperature (RT). On the basis of the VUV excitation spectra of MGd(PO₃)₄:1.0 at% Ce³⁺, the centroid shift ε_c, total crystal field splitting ε_cfs, and total redshift D(A) were calculated. According to the ligand polarization model, the values of the spectroscopic polarizability α_sp were also calculated from the observed centroid shifts. It was found that the ε_c, ε_cfs, D(A) and α_sp were influenced by the crystal structure. Based on the luminescence spectra of these polyphosphate samples, the energy level diagram of Gd³⁺–Ce³⁺ in MGd(PO₃)₄:Ce³⁺ systems was also proposed. Through the energy level diagram and the decay curves of Ce³⁺ emission, the energy transfer between Gd³⁺ and Ce³⁺ ions was investigated. It was found that there existed efficient energy transfer between Gd³⁺ and Ce³⁺ ions in MGd(PO₃)₄:Ce³⁺ systems. Considered the efficient energy transfer from Gd³⁺ to Ce³⁺ ions and short lifetime of Ce³⁺ emission, this series of compounds doped with Ce³⁺ ions could be used as promising scintillator materials.