Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO 4 ) 2 :Er 3+ /Yb 3+ with thermal management capability for silicon-based solar cells.

Raising photoelectric conversion efficiency and enhancing heat management are two critical concerns for silicon-based solar cells. In this work, efficient Yb 3+ infrared emissions from both quantum cutting and upconversion were demonstrated by adjusting Er 3+ and Yb 3+ concentrations, and thermo-manage-applicable temperature sensing based on the luminescence intensity ratio of two super-low thermal quenching levels was discovered in an Er 3+ /Yb 3+ co-doped tungstate system. The quantum cutting mechanism was clearly decrypted as a two-step energy transfer process from Er 3+ to Yb 3+ . The two-step energy transfer efficiencies, the radiative and nonradiative transition rates of all interested 4 f levels of Er 3+ in NaY(WO 4 ) 2 were confirmed in the framework of Föster-Dexter theory, Judd-Ofelt theory, and energy gap law, and based on these obtained efficiencies and rates the quantum cutting efficiency was furthermore determined to be as high as 173% in NaY(WO 4 ) 2 : 5 mol% Er 3+ /50 mol% Yb 3+ sample. Strong and nearly pure infrared upconversion emission of Yb 3+ under 1550 nm excitation was achieved in Er 3+ /Yb 3+ co-doped NaY(WO 4 ) 2 by adjusting Yb 3+ doping concentrations. The Yb 3+ induced infrared upconversion emission enhancement was attributed to the efficient energy transfer 4 I 11/2 (Er 3+ ) +  2 F 7/2 (Yb 3+ ) →  4 I 15/2 (Er 3+ ) +  2 F 5/2 (Yb 3+ ) and large nonradiative relaxation rate of 4 I 9/2 . Analysis on the temperature sensing indicated that the NaY(WO 4 ) 2 :Er 3+ /Yb 3+ serves well the solar cells as thermos-managing material. Moreover, it was confirmed that the fluorescence thermal quenching of 2 H 11/2 / 4 S 3/2 was caused by the nonradiative relaxation of 4 S 3/2 . All the obtained results suggest that NaY(WO 4 ) 2 :Er 3+ /Yb 3+ is an excellent material for silicon-based solar cells to improve photoelectric conversion efficiency and thermal management.