Luminescence of Er³⁺ doped oxyfluoride phosphate glasses and glass-ceramics

Glasses with the composition (75 NaPO₃-(25-x) CaO-xCaF₂) (in mol %) were prepared with 0.15 mol% of Er₂O_3. The effect of the glass composition and of heat treatment on the spectroscopic properties of the newly developed glasses is reported. With the progressive replacement of CaO by CaF₂, the Er³⁺:⁴I_13/2 lifetime and the intensity of the upconversion emission increase whereas the intensity of the emission at 1.5 μm decreases due to the decrease in the phonon energy in the as-prepared glasses. The glasses were heat treated at 20 °C above their respective glass transition temperature for 17 h to form nuclei and then at their crystallization temperature from 15min to 1 h to grow the nuclei into crystals. The heat treatment leads to the precipitation of crystalline phases, the composition of which depends upon the glass composition. As the Er³⁺:⁴I_13/2 lifetime increases and the intensity of the upconversion increases for the glass with x = 0 after heat treatment, the Er³⁺ ions are expected to be incorporated into the phosphate-based crystals. However, as the shape of the emission band at 1.5 μm remains unchanged and the intensity of the upconversion decreases significantly after heat treatment of the glasses with x > 10, the crystals found in the glass-ceramics with x > 10 are thought to free of Er³⁺ ions. Although Er³⁺ ions entered in the CaF₂ crystals precipitating in aluminosilicate glass, the Er³⁺ ions are believed to remain in the amorphous phosphate part of the glass-ceramic containing CaF₂ crystals.