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The efficiency of photovoltaic solar cells is strongly related to the spectral absorption and photo-conversion properties of the cell's active material, which does not exploit the whole broadband solar spectrum. This mismatch between the spectrum of the solar light and the wavelength dependent cell's response can be partially overcome by using luminescent conversion layers in front or in the back of the solar cell. In this paper, the investigation of Tb 3+ -Yb 3+ co-doped SiO 2 -HfO 2 glass and glass-ceramic waveguides is presented. Due to a down-conversion process based on cooperative energy transfer between one Tb 3+ ion and two Yb 3+ ions, a blue photon at 488 nm can be divided in two NIR photons at 980 nm. Films with different molar concentrations of rare earths, up to a total amount of [Tb + Yb] = 15%, were prepared by a sol-gel route, using dip-coating deposition on SiO 2 substrates. For all the films, the molar ratio [Yb]/[Tb] was taken equal to 4. The comparison of the energy-transfer efficiency between Tb 3+ and Yb 3+ ions in the glass and in the glass-ceramic materials demonstrated the higher performance of the glass-ceramic, with a maximum quantum transfer efficiency of 179% for the highest rare earth doping concentration. Moreover, experimental results and comparison with proper rate equations modelling showed a linear dependence of the photoluminescence emission intensity for the Yb 3+ ions 2 F 5/2 → 2 F 7/2 transition at 980 nm on the excitation power, indicating a direct transfer process from Tb 3+ to Yb 3+ ions. The reported waveguides could find applications not only as downconverting filters in transmission but also as efficient solar concentrators in the near-IR spectral region. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the possibility to obtain an efficient downconverting waveguide which combines the quantum cutting properties of Tb 3+ /Yb 3+ codoped materials with the optical sensitizing effects provided by silver doping. The preparation of 70SiO 2 –30HfO 2 glass and glass-ceramic waveguides by sol-gel route, followed by Ag doping by immersion in molten salt bath is reported. The films were subsequently annealed in air to induce the migration and/or aggregation of the metal ions. Results of compositional and optical characterization are given, providing evidence for the successful introduction of Ag in the films, while the photoluminescence emission is strongly dependent on the annealing conditions. These films could find potential applications as downshifting layers to increase the efficiency of PV solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Eu(dbm)3phen and Tb(dbm)3phen complexes (tris(dibenzoylmethane) mono(1,10-phenantroline) Ln(III)) were impregnated in ordered mesoporous silica nanoparticles (MSNs) with an average size of 50–70 nm and a pore diameter centred at 2.8 nm, with the aim of increasing the luminescence by avoiding concentration quenching and having mainly in mind the application as down-shifter for multi-crystalline solar cells. The morphological, structural, textural and luminescent properties of the synthesized samples were characterized by N2 adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–visible spectroscopy and photoluminescence measurements. It is demonstrated that inclusion in the MSNs allows one to use much higher loadings (23 wt%) of the Eu-complex than in other matrices, and that co-doping with Tb(dbm)3phen improves luminescence for samples with Eu(dbm)3phen content lower than about 10 wt%. Results are interpreted by using a simple sphere of action model adapted to the case of a pore-limited system. [Copyright &y& Elsevier]

Abstract: Terbium doped lanthanum aluminate (LaAlO3) nanophosphors were successfully synthesized by a combustion process using concentrated solution of lanthanum nitrates and aluminate as oxidiser, and glycine acid as fuel. The powders were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence spectroscopy. Pure LaAlO3 phase was obtained at 800°C heated for 4h, without formation of any intermediate phase, with an average crystal size, as determined by TEM, of 60nm. Intense green emission is reported at 542nm, from the level, which intensity depends on Tb concentration. [Copyright &y& Elsevier]