Glass transition-driven modulation of electron-phonon coupling and luminescence in wide-bandgap γ-Ga2O3 nanocrystals in glass-ceramics

Many properties of nanocrystals are modified by incorporation in glass, but little is known on glass transition effects. Here, for the first time, we report photoluminescence measurements up to and beyond the glass transition temperature of the amorphous matrix of a high-melting-temperature glass-ceramic incorporating wide-band-gap nanocrystals. The results – collected on γ-Ga2O3 nanocrystals in alkali-germanosilicate glass up to 873 K – give unprecedented evidence of spectroscopic changes at the glass transition. Nanocrystal photoluminescence unveils slope discontinuities in the temperature dependence of intensity, spectral position, and bandwidth. The results are analysed within a configurational model and with the aid of data from resonant and non-resonant Raman spectra at 266, 488, and 633 nm, providing estimations of acceptor ionization energy (0.42 eV) and involved phonon energy (50 meV). The data suggest that the acceptor ionization energy is reduced (by 70 meV) by increased structural mobility and dielectric screening at the glass transition.