Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO₄)₂:Er³⁺/Yb³⁺ 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 F & ouml;ster-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 I-4(11/2) (Er3+) + F-2(7/2) (Yb3+) -> I-4(15/2) (Er3+) + F-2(5/2) (Yb3+) and large nonradiative relaxation rate of I-4(9/2). 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 H-2(11/2)/S-4(3/2) was caused by the nonradiative relaxation of S-4(3/2). 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.