Abstract
Improving photoelectric conversion efficiency and enhancing heat management are two critical considerations for silicon-based solar cells. In this study, efficient ${{\rm Yb}^{3 +}}$ infrared emissions through the upconversion process were achieved by adjusting the concentrations of ${{\rm Yb}^{3 +}}$ in ${{\rm Er}^{3 +}}$ highly condensed ${\rm NaEr}{({{\rm WO}_4})_2}$ phosphor. Additionally, the temperature sensing based on the fluorescence intensity ratio (FIR) was also studied in this tungstate system. Moreover, the radiative transition rates for all relevant transitions of ${{\rm Er}^{3 +}}$ in ${\rm NaEr}{({{\rm WO}_4})_2}{:}{{\rm Yb}^{3 +}}$ phosphors were calculated in the framework of Judd-Ofelt theory, and the optical transition properties of ${{\rm Yb}^{3 +}}$ were also revealed by taking ${{\rm Er}^{3 +}}$ as a reference. It was found that the radiative transition rate of ${{\rm Yb}^{3 +}}{:}{^2}{{\rm F}_{5/2}}\,{\to}\, ^2{{\rm F}_{7/2}}$ (${2977.52}\;{{\rm s}^{- 1}}$) is significantly higher than that of ${{\rm Er}^{3 +}} {:}{^4}{{\rm I}_{11/2}}\,{\to}\, ^4{{\rm I}_{15/2}}$ (${303.50}\;{{\rm s}^{- 1}}$), thus suggesting the feasibility for the strong emission at 980 nm of ${{\rm Yb}^{3 +}}$ in assistance of the energy transfer $^4{{\rm I}_{11/2}} + {^2}{{\rm F}_{7/2}}\,{\to}\, ^4{{\rm I}_{15/2}} + {^2}{{\rm F}_{5/2}}$. Finally, strong and nearly pure NIR emissions of ${{\rm Yb}^{3 +}}$ were experimentally observed under 1550 nm excitation, and possible upconversion mechanisms were proposed. The temperature sensing performance of the studied materials was also assessed. All the results imply that ${\rm NaEr}{({{\rm WO}_4})_2}{:}{{\rm Yb}^{3 +}}$ constitutes an excellent material for enhancing both the photoelectric conversion efficiency and thermal management of silicon-based solar cells.
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