Energy transfer of Tm3+-Er3+ couples in NaYF4 microcrystals

Energy up- and down-conversions are two efficient methods to resolve spectral mismatch. This paper reports down-conversions in solar cells based GaAs. The energy is transfered from Tm3+1I6 → 1G4 749 nm (13356 cm-1) transition to Er3+4I9/2 → 4I15/2, 796 nm (12563 cm-1) by the cross relaxations, under excitation of Tm3+3H6 → 1I6, 294 nm (34364 cm-1), where the 1G4 level is used as an intermediate state. Then a high energy ultraviolet photon 294 nm can be cut into a near infrared 796nm photon and a blue 476 nm photon. Energy transfer efficiency and quantum cutting efficiency were estimated with experimental data. The spectral mismatch can be improved by the quantum cutting to enhance the conversion efficiency of solar cells.