Near-infrared luminescence and energy transfer in CaMoO4: Ho3+, Yb3+ phosphor

Down-conversion (DC) is a promising avenue to break Shockley–Queisser detailed balance limit, and efficient DC from one ultraviolet visible photon to two near-infrared (NIR) photons is realized in the Ho³⁺ –Yb³⁺ co-doped CaMoO₄ system. The scheelite samples have been synthesized via solid-state reaction method. Upon blue light excitation (447 nm), Ho³⁺ transfers its energy to Yb³⁺ via resonant cross-relaxation process, bringing about NIR luminescence. The visible emissions decrease as a function of Yb³⁺ contents, while NIR emission at 996 nm first increases and then decreases due to CQ at Yb³⁺ contents beyond 15 mol %. The lifetime of Ho³⁺: ⁵F₄, ⁵S₂ → ⁵I₈ with various Yb³⁺ contents is calculated as 114, 85, 73, 70, 64, 59 and 55 μs, respectively. The maximum energy transfer efficiency and the corresponding DC quantum efficiency are estimated to be 48 and 148 %. The phosphor may be a potential candidate for application in enhancing the performance of crystalline silicon solar cells.