Energy transfer mechanisms in Tb3+, Yb3+ codoped Y2O3 downconversion phosphor

Tb3+ and Yb3+ co-activated luminescent material that can cut one photon of around 483 nm into two NIR photons of around 1000 nm could be used as a downconversion luminescent convertor in front of crystalline silicon solar cell panels to reduce thermalization loss of the solar cell. The Tb3+ → Yb3+ energy transfer mechanisms in the UV-blue region in Y2O3 phosphor were studied by PL excitation spectra and time-resolved luminescence, from which the charge transfer mechanism and the cooperative transfer mechanism were identified. Tb3+ ions in the 4f75d1 state relax down to the 5D4 level and cooperatively transfer energy to two Yb3+ ions, which is followed by the emission of two photons (λ ∼ 1000 nm). It was found in the (Y0.79Tb0.01Yb0.20)2O3 sample that 37% of the Tb3+ ions at the 5D4 level transfer energy to two neighbouring Yb3+ ions by the cooperative energy transfer mechanism Tb3+ (5D4) → 2Yb3+ (2F5/2). Unfortunately, the high Yb3+ concentration leads to severe concentration quenching that significantly reduces the external quantum efficiency. Moreover, the energy of the Tb3+ 4f75d1 state can also be lost non-radiatively or transferred to the Yb3+2F5/2 state via the charge transfer state Tb4+-Yb2+. In conclusion, RE3+ (RE = Ce, Pr, Tb) with strong absorption in the UV region is not an appropriate sensitizer of Tb3+ in Tb3+-Yb3+ codoped downconversion phosphor