Ag-Sensitized NIR-Emitting Yb3+-Doped Glass-Ceramics

Featured Application downshifting layers for silicon solar cells, NIR emitting devices and lasers. Abstract The optical photoluminescent (PL) emission of Yb3+ ions in the near infrared (NIR) spectral region at about 950-1100 nm has many potential applications, from photovoltaics to lasers and visual devices. However, due to their simple energy-level structure, Yb3+ ions cannot directly absorb UV or visible light, putting serious limits on their use as light emitters. In this paper we describe a broadband and efficient strategy for sensitizing Yb3+ ions by Ag codoping, resulting in a strong 980 nm PL emission under UV and violet-blue light excitation. Yb-doped silica-zirconia-soda glass-ceramic films were synthesized by sol-gel and dip-coating, followed by annealing at 1000 degrees C. Ag was then introduced by ion-exchange in a molten salt bath for 1 h at 350 degrees C. Different post-exchange annealing temperatures for 1 h in air at 380 degrees C and 430 degrees C were compared to investigate the possibility of migration/aggregation of the metal ions. Studies of composition showed about 1-2 wt% Ag in the exchanged samples, not modified by annealing. Structural analysis reported the stabilization of cubic zirconia by Yb-doping. Optical measurements showed that, in particular for the highest annealing temperature of 430 degrees C, the potential improvement of the material's quality, which would increase the PL emission, is less relevant than Ag-aggregation, which decreases the sensitizers number, resulting in a net reduction of the PL intensity. However, all the Ag-exchanged samples showed a broadband Yb3+ sensitization by energy transfer from Ag aggregates, clearly attested by a broad photoluminescence excitation spectra after Ag-exchange, paving the way for applications in various fields, such as solar cells and NIR-emitting devices.