Downconversion in Y2Si2O7: Pr3+, Yb3+ polymorphs for its possible application as luminescent concentrators in photovoltaic solar-cells

Polycrystalline powders α and β phases of Y2Si2O7 (yttrium disilicate) co-doped with Pr3+, Yb3+ ions have been prepared by the sol-gel method. The structural phase purity of obtained silicates has been confirmed by XRD measurements. The possible Pr3+→Yb3+ energy transfer mechanisms were analyzed in a function of Yb3+ concentration for both phases of Y2Si2O7. It was proven that the probability of downconversion (DC) process is strongly dependent on excitation power and Yb3+ concentration. From the power dependence of emission intensity analysis it was found that for low excitation power regimes DC process is responsible for Pr3+→Yb3+ energy transfer while above threshold power a cross relaxation process becomes dominant.