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 O_h⋯D_4h⋯O_h 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.