High-pressure fluorescence line narrowing of Eu(III)-doped sodium disilicate glass

High-pressure fluorescence line narrowing (HPFLN) has been used to characterize the local structure of Eu³⁺ ions in sodium disilicate glass up to 210 kbar. HPFLN spectra, measured at 77 K, were analyzed using crystal-field theory. As pressure was increased from ambient to approximately 40 kbar, a redshift of the ⁵D₀←⁷F₀ excitation band was accompanied by a simultaneous decrease in the Eu³⁺ site crystal-field strength and a lengthening of the fluorescence lifetime from approximately 2.3 to 2.4 ms. These trends were reversed above 40 kbar, as crystal-field strength increased with pressure and lifetime decreased linearly to approximately 1.4 ms at 210 kbar. The ⁵D₀←⁷F₀ excitation band broadened significantly above 70 kbar and continued to shift red above 150 kbar. HPFLN results are interpreted in terms of structural changes in the silicate glass matrix and compression of the Eu³⁺ bonding environment. Lifetime and intensity changes are attributed to a pressure-induced increase in the electron-phonon coupling to local vibrations. Pressure-induced crystal-field effects are used to deduce characteristics of high- and low-crystal-field-strength sites in ambient pressure glasses. Spectral and lifetime results for the sample released from high pressure show that a new local Eu³⁺ structure is formed during decompression.