Glasses with the composition (75 NaPO3-(25-x) CaO-xCaF2) (in mol %) were prepared with 0.15 mol% of Er2O3. 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+:4I13/2 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+:4I13/2 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.