CaMoO4:x%Yb3+ : A Novel Near-Infrared Quantum-Cutting Phosphors via Cooperative Energy Transfer

An efficient near-infrared (NIR) dowmconversion (DC) has been demonstrated in the CaMoO4:Yb3+ phosphors. Very strong NIR emission around 998 nm from the F-2(5/2) -> F-2(5/2) transition of the Yb3+ has been observed under ultraviolet excitation. A similar broad excitation band due to the absorption of the host CaMoO4 has been recorded when the NIR emission of Yb3+ and the visible molybdate (MoO42-) emission are monitored, which suggests an efficient energy transfer (ET) from the host to the Yb3+. The Yb3+ concentration-dependent luminescence properties and lifetimes of both the visible and NIR emissions have also been studied. The lifetime of the molybdate emission decreases rapidly with the increasing Yb3+ concentration, further verifying the efficient ET from the host to the Yb3+. Moreover, the low temperature measurements have also been carried out to investigate the ET mechanism in the phosphors. A cooperative energy transfer (CET) mechanism has been proposed to rationalize the DC effect. The newly studied CaMoO4:Yb3+ DC phosphors, which can convert the broadband emission of the MoO42- into NIR emission of Yb3+ with a twofold increase in the photon number will have potential application in greatly enhancing the response of silicon-based solar cells with a relatively higher Yb3+ quenching concentration.