Light-emission enhancement in nanostructured gallium alkali-germanosilicate glasses
N.V. Golubev, E. S. Ignat’eva, V. N. Sigaev, R. Lorenzi, A. Paleari.
Glass-ceramics (GCs) with embedded nanocrystals (NCs) are one of the most promising material for photonic and optoelectronic applications. UV-excited light emission of Ga2O3-based GCs is of particular interest because Ga2O3 photoluminescence is accompanied by complete lacking of any excitation channel in the visible and near-UV spectrum. It permits the fabrication of solar-blind UV-to-visible converters based on GCs for monitoring UV-emitting events such as flames, electric sparks, and corona dispersions. The size of crystals in mentioned GCs is usually in the nanometer region. Thus, photoluminescence properties are expected to depend on the particle size. To fabricate GCs with optimal UV-to-visible conversion, data are needed about the relationships between nanostructure parameters (size, concentration) and luminescence efficiency.
In recent years Ga2O3-based silicate GCs doped with transition elements has been studied intensively due to their broadband near-infrared emission . In this field, we succeeded in the preparation of material with promising luminescent properties, based on germanosilicate GCs with gallium-containing spinel nanocrystals . Moreover, we described the thermal evolution of native nanoinhomogeneities in Ni2+-doped Ga-containing alkali-germanosilicate, based on SANS data, high resolution electron microscopy and infrared photoluminescence spectroscopy . Detected nanostructures were found to be responsible for the appearance of Ni-related near infrared luminescence with a band centered at 1300 nm and band-width exceeding 300 nm.
At present, data on light emission properties in the visible of undoped nanosized Ga oxides are mainly available for nanopowders and nanowires, or NCs in colloidal solutions . A large fraction of those results regard the β-Ga2O3 phase, whereas only few studies concern the metastable polymorph γ-Ga2O3. Only in a recent paper we describe the intrinsic light emission of γ-Ga2O3 NCs dispersed in glass matrices . We have found a novel and unexplored effect of spatial confinement on the donor-acceptor pair (DAP) recombination process when the nanocrystal size becomes comparable with the donor Bohr radius, and not too a low number of acceptors occur in the single nanocrystal. This confinement of DAP recombination depends strongly on the size of γ-Ga2O3 NCs and can enhance NCs photoluminescence in the case of exactly balanced DAPs. Such a system could in principle be tailored by controlling the nucleation process, which in turn determines concentration and size of undoped γ-Ga2O3 NCs and the resulting luminescence efficiency.
Our data show that luminescence is influenced not only by NC size change, and consequent modification of NC number density, but also by acceptor formation and passivation of Ga vacancies. In such processes, the interaction between the nanophase and the glass matrix plays a key role, providing the conditions for the occurrence of NC nucleation, NC coalescence, and Li incorporation, with a balance that depends on the nucleation temperature. These findings give a new direction to design transparent GCs with enhanced luminescent efficiency of embedded wide-band-gap NCs.
1. Yu Teng, Kaniyarakkal Sharafudeen, Shifeng Zhou and Jianrong Qiu. Glass-ceramics for photonic devices. Journal of the Ceramic Society of Japan 120 (2012) 458.
2. V.N. Sigaev, N.V. Golubev, E.S. Ignat’eva, V.I. Savinkov, M. Campione, R. Lorenzi, F. Meinardi, A. Paleari. Nickel-assisted growth and selective doping of spinel-like gallium oxide nanocrystals in germano-silicate glasses for infrared broadband light-emission. Nanotechnology 23 (2012) 015708/1-7.
3. V.N. Sigaev, N.V. Golubev, E.S. Ignat'eva, B. Champagnon, D. Vouagner, E. Nardou, R. Lorenzi, Alberto Paleari. Native amorphous nanoheterogeneity in gallium germanosilicates as a tool for driving Ga2O3 nanocrystal formation in glass for optical devices. Nanoscale 5 (2013) 299.
4. S. Kumar, R. Singh. Nanofunctional gallium oxide (Ga2O3) nanowires/nanostructures and their applications in nanodevices. Phys. Status Solidi RRL 7 (2013) 781.
5. V.N. Sigaev, N.V. Golubev, E.S. Ignat’eva, A. Paleari, R. Lorenzi. Light-emitting Ga-oxide nanocrystals in glass: a new paradigm for low-cost and robust UV-to-visible solar-blind converters and UV emitters. Nanoscale 6 (2014) 1763.