Nephelauxetic effect of the hydride ligand in Sr2LiSiO4H as a host material for rare-earth-activated phosphors

Abstract

Strontium lithium orthosilicate hydride Sr₂LiSiO₄H was synthesized by the reaction of Sr₂SiO₄ with LiH at 700 °C in a H₂ rich atmosphere. Rietveld refinement of the neutron powder diffraction pattern revealed that Sr₂LiSiO₄H is isostructural to Sr₂LiSiO₄F (space group P2₁/m) and its channel-like structure preferentially accommodates H⁻ ions over F⁻ ions. In addition, Sr₂LiSiO₄H is stable in air and its Eu²⁺-doped analog exhibits yellow photoluminescence with an emission band at 544 nm and a broad excitation band ranging from 250 to 450 nm. These bands were observed in the longer wavelength region when compared with those displayed by Sr₂LiSiO₄F:Eu²⁺. The red shift, which is induced by H⁻ substitution, is consistent with the constrained density functional theory calculations, predicting the photo-excitation and emission energies of 4f–5d transitions. The present study reports the synthesis of stable oxyhydrides acting as phosphor hosts for rare earth ions. The phosphor hosts exhibit large nephelauxetic effects owing to the presence of H⁻ ligands.