Enhanced near-infrared quantum cutting in CaMoO₄:Yb³⁺ phosphors induced by doping with Li⁺ ions for improving solar cells efficiency

The near-infrared (NIR) quantum cutting (QC) CaMoO₄:Yb ³⁺ phosphors co-doped with Li⁺ ions were synthesized by the sol-gel methods. The dependence of the structure, morphology, photoluminescence (PL) and downconversion (DC) quantum efficiency on the Li ⁺ doping concentration have been investigated in details. It was demonstrated that the CaMoO₄:Yb³⁺ phosphors with appropriate concentration of the Li⁺ ions show improved crystallinity and remarkable increase of the NIR emission from the Yb³⁺ ions, if compared with the Li⁺-free samples. The enhancement of the NIR emission and DC quantum efficiency was suggested to be a consequence of the improved crystallinity and stronger absorption of the host due to the [MoO ₄] tetrahedra distortion induced by the Li⁺ ions. Cooperative energy transfer (CET) from the host to the Yb³⁺ ions is discussed as a possible mechanism for the NIR emission enhancement. Excellent luminescence properties of the Li⁺ doped CaMoO₄:Yb ³⁺ phosphor demonstrate its potential application as a better QC layer to increase the energy conversion efficiency of the Si-based solar cells.