Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO):Er/Yb 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 infrared emissions from both quantum cutting and upconversion were demonstrated by adjusting Er and Yb 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/Yb co-doped tungstate system. The quantum cutting mechanism was clearly decrypted as a two-step energy transfer process from Er to Yb. The two-step energy transfer efficiencies, the radiative and nonradiative transition rates of all interested 4 f levels of Er in NaY(WO) 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): 5 mol% Er/50 mol% Yb sample. Strong and nearly pure infrared upconversion emission of Yb under 1550 nm excitation was achieved in Er/Yb co-doped NaY(WO) by adjusting Yb doping concentrations. The Yb induced infrared upconversion emission enhancement was attributed to the efficient energy transfer I (Er) + F (Yb) → I (Er) + F (Yb) and large nonradiative relaxation rate of I. Analysis on the temperature sensing indicated that the NaY(WO):Er/Yb serves well the solar cells as thermos-managing material. Moreover, it was confirmed that the fluorescence thermal quenching of H/S was caused by the nonradiative relaxation of S. All the obtained results suggest that NaY(WO):Er/Yb is an excellent material for silicon-based solar cells to improve photoelectric conversion efficiency and thermal management.