Novel Dy3+-doped Ge4+-substituted apatite-type phosphors, Ca9La(PO4)5[(Si1-xGexO4)]F2:Dy3+: Synthesis, structure, crystal chemical features, and luminescent properties

Abstract

The series of novel phosphors Ca9La(PO4)5 [(Si1-xGexO4)]F2:0.15Dy3+ with x = 0, 0.25, 0.50, 0.75 and 1 (CLPS1-xGxF:0.15Dy3+) with apatite-type structure (space group P63/m) has been synthesized. The crystal structure and electronic structure have been studied by powder X-ray diffraction (PXRD) in combination with the atomic-scale density functional theory (DFT) calculations. A combination of Raman, nuclear magnetic resonance (29Si NMR) spectroscopy and the evolution of Dy3+ ions photoluminescent properties was used to characterize the local crystal structure features. Based on the variation of the [SiO4] by [GeO4] tetrahedral substitutions in the apatite-type structure, the difference in the thermal stability and decay curves of CLPS1-xGxF:0.15Dy3+ phosphors were referred to crystal chemical stability of as-prepared compounds, which is also confirmed by the values of polyhedral distortion, bond valence sum (BVS) and DFT calculations. The present study provides new insights the synthetic methodology and fundamental characterizations into the design of new phosphors combined with theoretical methods.