Cubic and Hexagonal NaGdF₄ Crystals Precipitated from an Aluminosilicate Glass: Preparation and Luminescence Properties

Abstract

Depending on the composition of the glass and the annealing procedure supplied, thermal annealing of silicate glasses in the system SiO2/Al2O3/AlF3/Na2O/Gd2O3/SmF3 led to the precipitation of cubic or hexagonal NaGdF4 nanocrystals. The glasses were already phase separated after casting and formed a droplet phase supposedly enriched in fluorides and rare earths. The droplets had sizes mainly in the range from 80 to 120 nm. During annealing at temperatures ≥600 °C, multicore particles of cubic or hexagonal NaGdF4 were precipitated inside the amorphous droplet phase. Completely transparent hexagonal NaGdF4 containing nano-glass-ceramics could be derived from this system. Fluorescence spectra and fluorescence decay curves of Sm3+ show crystal phase dependent effects. Sm3+ doped hexagonal NaGdF4 exhibits notably different fluorescence emission spectra and longer fluorescence lifetimes than cubic NaGdF4.