γ-Ga2O3 nanocrystals in germano-silicate glass as multipurpose photonic material

The ability to incorporate crystalline nanostructures in amorphous glass is a successfully strategy for the design of novel functional and structural materials. On the one hand, the oxide matrix ensures ideal workability, chemical inertness, and mechanical robustness. On the other hand, crystalline nanoparticles may give rise to unprecedented optical, electrical, or mechanical behaviour. In this view, alkali germano-silicate glasses containing γ-Ga2O3 nanoparticles, prepared by the melt-quenched method, represent an interesting solution as multipurpose photonic materials. In fact, the low refractive mismatch between crystals and matrix as well as the ability of obtaining nanostructures with dimensions of the order of few nanometers enables the possibility of having a transparent material with peculiar optical properties. γ-Ga2O3 is indeed a wide-band gap semiconductor (EG = 4.9 eV) showing strong blue luminescence upon excitation at wavelength shorter than 280 nm and related to recombination at donor and acceptor pairs. For these reasons Ga2O3-based materials would be particularly suitable, in principle, for the fabrication of simple and robust UV-to-visible converters. The photoluminescence excitation threshold at 280 nm coincides with the UV-C region above which the solar spectrum does not give any background to the detection of UV-emitting events such as flames, electric sparks, and corona dispersions, which can significantly affect safety conditions in working places, energy-saving, and electric power distribution reliability. Beyond this intrinsic luminescence, γ-Ga2O3 may also host other optically-active ions so as to enrich the photophysics of the system. Here we present our recent results on the optimization of the intrinsic emission features of these glassceramics and their application as UV-light converter in solar-blind passive devices. Moreover, we also discuss the optical behaviour of samples doped with rare-earth and transition metal ions. In particular, we will focus on samples doped with Nickel ions that show strong broadband infrared emission, and Gadolinium doped samples where energy-transfer processes take place thus enabling rare-earth emission with large excitation cross section.