The nano-crystallization and fluorescence of terbium doped Na2O/K2O/CaO/CaF2/Al2O3/SiO2 glasses

Oxyfluoride glasses with the molar composition 59.3 SiO2 center dot 3.7 Al2O3 center dot 12.3 CaO center dot 5.3 K2O center dot 9.0 Na2O center dot 10.4 CaF2 were doped with different Tb3+-concentrations (1 x 10(19), 5 x 10(19) and 1 x 10(20) cm(-3)). The glasses were thermally treated in the temperature range from 550 to 600 degrees C, which resulted in the crystallization of cubic CaF2. The XRD-patterns showed extremely broadened lines attributed to mean crystallite sizes in the range from 11 to 15 nm. SEM and TEM micrographs showed polycrystalline particles with a size of around 200 nm which are composed of smaller, about 15 nm large, crystallites. Static fluorescence spectra as well as fluorescence decay curves were recorded for samples with different TbF3-concentrations and different thermal treatment. For samples with a low Tb3+ doping concentration notably prolonged fluorescence lifetimes were measured.