Time-resolved luminescence study of CaF2:Eu2+ nanocrystals in glass-ceramics

CaF2:Eu2+ nanocrystals are prepared by heating 45SiO2-20Al2O3-10CaO-25CaF2-0.1Eu2O3 glasses above Tg=630 °C. The size of grown crystals in glass-ceramics appears to be 5-35 nm from XRD and TEM measurements, depending on the heating temperature and holding time. Time-resolved luminescence spectra due to Eu2+ ions are measured at 77 and 300 K under the excitation with the third harmonics of a Nd:YAG laser. It is found that the main band peaking at 2.97 eV in glass-ceramics at delay time τD=0 μs is high-energy shifted by 0.04 eV relative to that of CaF2:Eu2+ single crystals. When τD increases to 9 μs, a new band is observed at around 2.7 eV in both glass and glass-ceramics. On the basis of the present results, the formation process and luminescence properties of nanosized CaF2:Eu2+ crystals in glass-ceramics are discussed.