Structure and distortion of lead fluoride nanocrystals in rare earth doped oxyfluoride glass ceramics
Abstract
A series of rare earth (RE) doped oxyfluoride glasses with the composition of (45-x) SiO2–5Al2O3–40PbF2–10CdF2–xRe2O3 (x = 1, 5, 10, 15) (mol%) were prepared by a traditional melt-quenching method. Glass ceramics (GCs) were obtained after thermal treatment and characterized by X-ray diffraction (XRD) to investigate the nanocrystal structure and distortion. Both the dopant type and the doping level play an important role in the distortion of the PbF2–RE lattice. It is found that a cubic Pb3REF9 phase forms in low doping GCs, a tetragonal PbREF5 phase forms in middle doping GCs and cubic PbRE3F11 forms in high doping GCs. Accordingly, the site symmetry of RE3+ dopants in β-PbF2 nanocrystal undergoes a transition of Oh⋯D4h⋯Oh with the increase of doping level. The change in the ligands coordinating the RE3+ ions was further illustrated by the optical changes in Yb-doped GCs. This paper provides insights on the nanocrystal structure of RE at the atomic level and tries to make a complete description of the nanocrystal structure and distortion in these glass–ceramic materials, which will benefit the optimization of optical properties.