Near-infrared quantum cutting and energy transfer mechanism in Lu2O3:Tm3+/Yb3+ phosphor for high-efficiency photovoltaics

Near-infrared downconversion phenomenon has been demonstrated in Lu2O3: Tm3+/Yb3+ phosphor upon direct excitation of Tm(3+:1)G(4) level at 463 nm. The efficient energy transfer from Tm3+: (1)G(4) -> Yb: F-2(5/2) has been elucidated by the excitation spectra, the visible and NIR spectra as well as the decay curves of Tm: (1)G(4) state. The mechanism of downconversion in Lu2O3: Tm3+/Yb3+ has been discussed in detail. According to analysis of the dependence of the initial transfer rate over Yb3+ ion concentration, it could be included that energy transfer (ET) from Tm3+ to Yb3+ is a single-step ET process instead of a cooperative one. By varying the Yb3+ concentrations, we obtain the Lu2O3: 0.2% Tm3+/30%Yb3+ sample with theoretical quantum efficiency as high as 148.2%. Because the excited state of Yb3+ just above the band edge of crystalline silicon, it suggested that Lu2O3: Tm3+/Yb3+ sample will be beneficial to improve the conversion efficiency of c-Si solar cells.