Luminescence behaviour of Eu³⁺ in hot-compressed silicate glasses

This paper aims to explore density-driven effects on the luminescence of Eu³⁺ doped silicate glasses. For this, mildly densified samples were fabricated by quasi-isostatic hot compression at up to 2 GPa from melt-quenched precursor materials. As a result of compression, both density and glass transition temperature of the blank (Eu free) and doped compositions increase. Raman spectroscopy indicates a slight increase in the intensity of vibrational modes assigned to small silicate rings and Si-O-Si bridges. Photoluminescence experiments reveal the creation of new paths of de-excitation, reducing the relative intensity of the transitions in the excitation spectra and the lifetime of the ⁵D₀ → ⁷F₂ emission line. Meanwhile, the luminescence intensity remains unchanged due to enhanced oscillator strength and refractive index at uniform electron-phonon coupling strength. Luminescence spectra also show a slight expansion of some of the energy levels of Eu³⁺, together with an increase of the bandwidth of the ⁵D₀ → ⁷F₂ emission line due to the crystal-field influence and growing electron population of the lower Stark sub-levels. Finally, increasing symmetry of Eu³⁺ sites was detected with increasing degree of compaction, resulting in a reduction of the intensity of the forced electric dipole transition of ⁵D₀ → ⁷F₂ relative to the magnetic dipole transition of ⁵D₀ → ⁷F₁.