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
Duan Gao, Baojiu Chen, Xuezhu Sha, Yuhang Zhang, Xin Chen, Li Wang, Xizhen Zhang, Jinsu Zhang, Yongze Cao, Yichao Wang, Lei Li, Xiangping Li, Sai Xu, Hongquan Yu, Lihong Cheng
Abstract
Abstract 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.