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 Yb3+ infrared emissions from both quantum cutting and upconversion were demonstrated by adjusting Er3+ and Yb3+ concentrations, and thermo-manage-applicable temperature sensing based on the luminescence intensity ratio of two super-low thermal quenching levels was discovered in an Er3+ /Yb3+ co-doped tungstate system. The quantum cutting mechanism was clearly decrypted as a two-step energy transfer process from Er3+ to Yb3+ . The two-step energy transfer efficiencies, the radiative and nonradiative transition rates of all interested 4 f levels of Er3+ in NaY(WO4 )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(WO4 )2 : 5 mol% Er3+ /50 mol% Yb3+ sample. Strong and nearly pure infrared upconversion emission of Yb3+ under 1550 nm excitation was achieved in Er3+ /Yb3+ co-doped NaY(WO4 )2 by adjusting Yb3+ doping concentrations. The Yb3+ induced infrared upconversion emission enhancement was attributed to the efficient energy transfer 4 I11/2 (Er3+ ) + 2 F7/2 (Yb3+ ) → 4 I15/2 (Er3+ ) + 2 F5/2 (Yb3+ ) and large nonradiative relaxation rate of 4 I9/2 . Analysis on the temperature sensing indicated that the NaY(WO4 )2 :Er3+ /Yb3+ serves well the solar cells as thermos-managing material. Moreover, it was confirmed that the fluorescence thermal quenching of 2 H11/2 /4 S3/2 was caused by the nonradiative relaxation of 4 S3/2 . All the obtained results suggest that NaY(WO4 )2 :Er3+ /Yb3+ is an excellent material for silicon-based solar cells to improve photoelectric conversion efficiency and thermal management.