Near infrared quantum cutting by cooperative energy transfer from Tb³⁺ to Yb³⁺ in YPO₄

Near infrared quantum cutting by cooperative energy transfer from Tb³⁺ to Yb³⁺ was investigated by photoluminescence measurements on (Yb_xY_1−x)PO₄ (x = 0, 0.05, 0.1, 0.15) doped with 1 % Tb³⁺. Under the excitation of 473 and 486 nm continuous wave lasers, we found that one Tb³⁺ ion absorbed one blue photon with the transition from ⁵D₄ to ⁷F₅ (λ ~ 544 nm) and cooperatively transfer energy to Yb³⁺ ions, which is followed by the emission of two photons (λ ~ 980 nm). Application of cooperative energy transfer has prospects for increasing the energy efficiency of crystalline Si solar cells by photon doubling of the high energy part of the solar spectrum.