Energy transfer mechanisms in Tb³⁺, Yb³⁺codoped Y₂O₃downconversion phosphor

Tb 3+ and Yb 3+ 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 Tb 3+ → Yb 3+ energy transfer mechanisms in the UV–blue region in Y 2 O 3 phosphor were studied by PL excitation spectra and time-resolved luminescence, from which the charge transfer mechanism and the cooperative transfer mechanism were identified. Tb 3+ ions in the 4f 7 5d 1 state relax down to the 5 D 4 level and cooperatively transfer energy to two Yb 3+ ions, which is followed by the emission of two photons (λ ∼ 1000 nm). It was found in the (Y 0.79 Tb 0.01 Yb 0.20 ) 2 O 3 sample that 37% of the Tb 3+ ions at the 5 D 4 level transfer energy to two neighbouring Yb 3+ ions by the cooperative energy transfer mechanism Tb 3+ ( 5 D 4 ) → 2Yb 3+ ( 2 F 5/2 ). Unfortunately, the high Yb 3+ concentration leads to severe concentration quenching that significantly reduces the external quantum efficiency. Moreover, the energy of the Tb 3+ 4f 7 5d 1 state can also be lost non-radiatively or transferred to the Yb 3+ 2 F 5/2 state via the charge transfer state Tb 4+ –Yb 2+ . In conclusion, RE 3+ (RE = Ce, Pr, Tb) with strong absorption in the UV region is not an appropriate sensitizer of Tb 3+ in Tb 3+ –Yb 3+ codoped downconversion phosphor.