Spectroscopic Properties and Upconversion Studies in Ho3+/Yb3+ Co-doped Calcium Scandate with Spectrally Pure Green emission

The optical properties of a Ho3+/Yb3+ co-doped CaSc2O4 oxide material are investigated in detail. The spectral properties are described as a function of doping concentrations. The efficient Yb3+Ho3+ energy transfer is observed. The transfer efficiency approaches 50% before concentration quenching. The concentration-optimized sample exhibits a strong green emission accompanied with a weak red emission, showing perfect green monochromaticity. The results of the spectral distribution, power dependence, and lifetime measurements are presented. The green, red, and near-infrared (NIR) emissions around 545, 660, and 759 nm are assigned to the F-5(4)+(S2I8)-S-5-I-5, (F5I8)-F-5-I-5, and F-5(4)+(S2I7)-S-5-I-5 transitions of Ho3+, respectively. The detailed study reveals the upconversion luminescence mechanism involved in a novel Ho3+/Yb3+ co-doped CaSc2O4 oxide material.