Investigation of phase evolution and Gd occupation in (Lu1-xGdx)2SiO5 lattice by Rietveld refinement and DFT simulation

Abstract

Cerium-doped lutetium oxyorthosilicate (LSO:Ce, Lu2SiO5:Ce) is considered to be a typical scintillator with comprehensive good scintillation properties. The doping of Gd3+ elements with different concentrations strongly influences the structure and luminescence performance of LSO. The full concentration range of LGSO ((Lu1-xGdx)2SiO5) powders were prepared using a sol-gel method. The influences of the doping Gd3+ ion concentration on the phase evolution and lattice parameters of LGSO were investigated via X-ray diffraction (XRD), Rietveld refinement and density functional theory (DFT) simulations. It was found that the monoclinic crystal structure of LGSO gradually transitioned from C2/c to P21/c under elevated temperatures and phase transition temperature varied from 975 to 1400 ​°C as Gd replaced Lu. The lattice constants (a, b, and c) of LGSO lattice increased with the addition of Gd. The Rietveld refinement results indicate that doping Gd3+ in LGSO was prone to occupy the RE1 site rather than the RE2 site and Gd dopants was easily to form GdRE1-GdRE1 defect complex. The formation energy results of Gd3+ replacing different Lu3+ sites calculated by using the first-principles pseudopotential approach further proved this occupation mode. The intensity of photoluminescence of Ce:(Lu1-xGdx)2SiO5 attained the peak value when the content of Gd doping reached 0.05.