This study investigated photoluminescent properties of Sr2CaWO6:Yb3+, Na+ phosphor. The samples were successfully synthesized via a solid-state reaction method with various doping concentrations. The phosphorcan efficiently absorb ultraviolet photons of 250–350nm and transfer its absorbed photon energy toYb3+ions. Then subsequent quantum cutting betweenWO6 groups and Yb3+ions takes place, down-converting an absorbed ultraviolet photon into two photons of 1007nm radiations. Analyses of decay curves of different samples reveal an efficient energy transfer from WO6 groupsto Yb3+ions. Cooperative energy transfer from host to Yb3+ ions is responsible for downconversion via lifetime analysis. Quantum efficiencies were calculated, and estimated maximum efficiency reached 190%. These phosphors combine wide wavelength absorption in the ultraviolet range with high quantum efficiency, enabling potential application of efficiency enhancement ofSisolar cell.