Self-limited growth of Pr3+-doped LaF3 nanocrystals in oxyfluoride glass and glass-ceramics

Abstract

Transparent oxyfluoride glass-ceramics of heavy metals doped with rare earth metal ions are important materials in optoelectronics. In the present study, we report the preparation of a glass and a glass-ceramic with composition 16.52Al2O3·1.5 AlF3·12.65LaF3·4.33Na2O·64.85 SiO2 (mol%), where both the materials were doped with 1 mol% Pr2O3. All four species were structurally characterized by Transmission Electron Microscopy (TEM). Pr2O3 affected the phase separation in the glass and deferred crystallization compared to the undoped glass. The crystallization mechanism and the location of various components in the glass/glass-ceramics were ascertained through advanced STEM/EDX techniques. The phase separated regions in the mother glass were mostly populated by F and La and also by Pr, Al and Si. The phase separated droplets, after annealing, turned into 10-20 nm LaF3 nanocrystals, which were found to partly include the doping Pr3+ ions in the crystals themselves. The interphase crystal/glassy matrix was thoroughly characterized by EDX. The results suggest that the inner LaF3 crystal core is engulfed by an Al enriched layer that follows a Si enriched surrounding shell as the outer core. This finding also indicates that the crystal surface is too viscous to further enhance the crystal growth, and therefore the overall crystal formation is limited to the nanosize.