Efficient Near-Infrared Downconversion and Energy Transfer Mechanism of Ce3+/Yb3+ Codoped Calcium Scandate Phosphor

An efficient near-infrared (NIR) downconversion has been demonstrated in CaSc2O4: Ce3+/Yb3+ phosphor. Doping concentration optimized CaSc2O4: 1%Ce3+/5%Yb3+ shows stronger NIR emission than-doping concentration also optimized typical YAG: 1%Ce3+/5%Yb3+ under 470 nm excitation. The NIIR emission from 900 to 110 nm is enhanced by a factor Of 2.4. In addition; the main emission peak of Yb3+ in the CaSc2O4 around 976 nm, matches better with the optimal spectral response of the c-Si solar cell. The visible and NIR spectra and the decay curves of Ce3+: 5d -> 4f emission were used to demonstrate the energy transfer from Ce3+ ions to Yb3+ ions. The downconversion phenomenon has been observed under the direct excitation. of Ce3+ ions. On analyzing the dependence of energy transfer rate on Yb3+ ion concentration, we reveal that the energy transfer (ET) from Ce3+ ions to Yb3+ ions in CaSc2O4 occurs mainly by the single-step ET process. Considering that the luminescence efficiency of CaSc2O4: Ce3+ is comparable to that of commercial phosphor YAG: Ce3+, the estimated maximum energy transfer efficiency reaches 58% in the CaSc2O4: 1%Ce3+/15% Yb3+ sample, indicating that CaSc2O4: Ce3+/Yb3+ sample has the potential in improving the conversion efficiency of c-Si solar cells.