Enhanced Blue Emission from Transparent Oxyfluoride Glass-Ceramics Containing Pr3+:BaF2 Nanocrystals

Transparent glass-ceramics containing Pr3+:BaF2 nanocrystals in the chemical composition of SiO2-BaF2-K2CO3-La2O3-Sb2O3 oxyfluoride glass systems have been prepared from melt quenching and with a subsequent heat-treatment method. The luminescence and structural properties of these materials have been evaluated and the results are reported. Rietveld analysis of X-ray diffraction patterns and investigation of transmission electron microscopy confirmed the presence of BaF2 nanocrystals dispersed in the heat-treated glass matrices. Measured UV-Vis-NIR absorption spectra exhibited nine bands of the transitions 3H(4)-> 3P(2), (1I(6), 3P(1)), 3P(0), 1D(2), 1G(4), 3F(3), 3F(2), 3H(6), and 3H(5) from all the samples with nondegenerated 1I(6) and 3P(1) levels in the glass-ceramics. The photoluminescence spectra show an enhancement in the intensities upon ceramization, indicating the incorporation of Pr3+ ions into BaF2 nanocrystals that possess a low phonon energy (346 cm-1). This has further been corroborated from the observation of a significant threefold increase in the relative intensity ratio of blue (3P(0)-> 3H(4)) to red (1D(2)-> 3H(4), 3P(0)-> 3H(6)) emissions from glass-ceramics compared with the glass. This is due to a significant decrease of multiphonon nonradiative relaxation from the 3P(0) to the 1D(2) level of Pr3+ in glass-ceramics. Time-resolved spectra exhibit 3P(0)-level decays faster than the 1D(2) level.