Enhanced Blue Emission from Transparent Oxyfluoride Glass-Ceramics Containing Pr~(3+):BaF_2 Nanocrystals

摘要

Transparent glass-ceramics containing Pr~(3+):BaF_2 nanocrystals in the chemical composition of SiO_2-BaF_2-K_2CO_3-La_2O_3-Sb_2O_3 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 BaF_2 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 Pr~(3+) ions into BaF_2 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 Pr~(3+) in glass-ceramics. Time-resolved spectra exhibit ~3P_0-level decays faster than the ~1D_2 level.