Reddish-Orange Luminescence from BaF(2):Eu(3+) Fluoride Nanocrystals Dispersed in Sol-Gel Materials

Nanocrystalline transparent BaF(2):Eu(3+) glass-ceramic materials emitting reddish-orange light were fabricated using a low-temperature sol-gel method. Several experimental techniques were used to verify structural transformation from precursor xerogels to sol-gel glass-ceramic materials containing fluoride nanocrystals. Thermal degradation of xerogels was analyzed by thermogravimetric analysis (TG) and differential scanning calorimetry method (DSC). The presence of BaF(2) nanocrystals dispersed in sol-gel materials was confirmed by the X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). In order to detect structural changes in silica network during annealing process, the infrared spectroscopy (IR-ATR) was carried out. In particular, luminescence spectra of Eu(3+) and their decays were examined in detail. Some spectroscopic parameters of Eu(3+) ions in glass-ceramics containing BaF(2) nanocrystals were determined and compared to the values obtained for precursor xerogels. It was observed, that the intensities of two main red and orange emission bands corresponding to the (5)D(0)→(7)F(2) electric-dipole transition (ED) and the (5)D(0)→(7)F(1) magnetic-dipole (MD) transition are changed significantly during transformation from xerogels to nanocrystalline BaF(2):Eu(3+) glass-ceramic materials. The luminescence decay analysis clearly indicates that the measured lifetime (5)D(0) (Eu(3+)) considerably enhanced in nanocrystalline BaF(2):Eu(3+) glass-ceramic materials compared to precursor xerogels. The evident changes in luminescence spectra and their decays suggest the successful migration of Eu(3+) ions from amorphous silica network to low-phonon BaF(2) nanocrystals.