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 3H4→3P2, (1I6, 3P1), 3P0, 1D2, 1G4, 3F3, 3F2, 3H6, and 3H5 from all the samples with nondegenerated 1I6 and 3P1 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 (3P0→3H4) to red (1D2→3H4, 3P0→3H6) emissions from glass–ceramics compared with the glass. This is due to a significant decrease of multiphonon nonradiative relaxation from the 3P0 to the 1D2 level of Pr3+ in glass–ceramics. Time-resolved spectra exhibit 3P0-level decays faster than the 1D2 level.
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