Downconversion mechanism in Er3+/Yb3+ codoped fluorotellurite glasses to enhance the efficiency of c-Si PV cells

Fluorotellurite glass codoped with erbium and ytterbium was elaborated through the melting-quenching route. Through the DSC and Raman measurements, the investigated glass samples presented high thermal stability and low phonon energy, respectively. By using the laser excitation at 488 nm, the downconversion mechanism in the Er3+/Yb3+ system was investigated and the energy transfers implicated in the emissions of erbium and ytterbium ions were discussed based on the different cross-relaxation processes. The addition of ytterbium resulted in an effective energy transfer from the excited 4S3/2/2H11/2 state of Er3+ ions to the emitting 2F5/2 state of Yb3+ ion, which considerably enhanced NIR emissions at 1000 nm and reduced experimental lifetimes of  4S3/2/2H11/2 states. Through luminescence decay analysis, the maximum values of quantum efficiency (ηQE) and energy transfer efficiency (ηET) were estimated as 61.2% and 161.2%, respectively. This result indicates that the proposed glasses can convert visible photons into NIR emissions at 1000 nm suitable to improve the spectral response of crystalline silicon PV cells.