Nephelauxetic effect of the hydride ligand in Sr 2 LiSiO 4 H as a host material for rare-earth-activated phosphors

Abstract

Strontium lithium orthosilicate hydride Sr 2 LiSiO 4 H was synthesized by the reaction of Sr 2 SiO 4 with LiH at 700 °C in a H 2 rich atmosphere. Rietveld refinement of the neutron powder diffraction pattern revealed that Sr 2 LiSiO 4 H is isostructural to Sr 2 LiSiO 4 F (space group P2 1 /m) and its channel-like structure preferentially accommodates H − ions over F − ions. In addition, Sr 2 LiSiO 4 H is stable in air and its Eu 2+ -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 Sr 2 LiSiO 4 F:Eu 2+ . 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.