Distribution of thulium in Tm3+-doped oxyfluoride glasses and glass-ceramics

Rare-earth (RE) doped transparent glass-ceramics are presented as very promising materials for optical applications. In this work, Transmission Electron Microscopy techniques have been used to structurally characterize a glass of composition 55SiO(2)-20Al(2)O(3)-15Na(2)O-10LaF(3) (mol%), doped with 1 mol% Tm2O3, and the corresponding glass-ceramic. The proposed crystallization mechanism for this glass has been modified from the results obtained through advanced STEM/EDXS techniques. The parent glass contains phase separated regions mainly enriched in F and La and also in Al, Si and Tm. After annealing, 10-20 nm LaF3 nano-crystals are formed from these phase separated droplets. The partial incorporation of the doping Tm3+ ions into the LaF3 nano-crystals has been verified and the interphase crystal/glassy matrix has been more precisely characterized through EDXS. An Al enriched layer is formed around the crystals followed by a Si enriched shell, which greatly increase the viscosity in the periphery of the crystals, inhibiting further crystal growth and thus, keeping the nano size of the crystals.