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

Abstract

Oxyfluoride glasses with the molar composition 59.3 SiO₂·3.7 Al₂O₃·12.3 CaO·5.3 K₂O·9.0 Na₂O·10.4 CaF₂ were doped with different Tb³⁺-concentrations (1 × 10¹⁹, 5 × 10¹⁹ and 1 × 10²⁰ cm⁻³). The glasses were thermally treated in the temperature range from 550 to 600 °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.