Abstract
Tb4+-Yb3+ co-doped NaYF4 nanoparticles (NPs) are prepared by sintering the as-synthesized NaYF4:Tb3+, Yb3+ NPs at 380°C under air atmosphere. The oxidization of Tb3+ ions to Tb4+ ions in NaYF4 NPs after sintering is demonstrated through X-ray photoelectron spectroscopy (XPS). The near-infrared (NIR) downconversion (DC) luminescence of Tb4+-Yb3+ couple is measured and investigated for the first time. The results show that DC luminescence of Tb4+-Yb3+ couple enhance obviously compared with Tb3+-Yb3+ couple in as-synthesized sample. The enhancement factor is about 14 and 19 excited at 379nm and 487nm, respectively. On analyzing the exponential dependence of NIR fluorescence intensity on the pumping power, we reveal that the energy transfer (ET) mechanism from Tb4+ to Yb3+ in NaYF4 NPs occurs by the single-step ET process. Our study may provide a promising DC layer on the top of silicon-based solar cells to improve the photovoltaic conversion efficiency.
Highlights
The increasing demand for solar energy, due to its green and inexhaustible advantage, has put how to improve the photovoltaic conversion efficiency of solar cells at the forefront of research [1]
On analyzing the exponential dependence of NIR fluorescence intensity on the pumping power, we reveal that the energy transfer (ET) mechanism from Tb4+ to Yb3+ in NaYF4 NPs occurs by the single-step ET process
We reveal that the energy transfer (ET) mechanism from Tb4+ ions to Yb3+ ions in NaYF4 NPs occurs by the single-step ET process through the exponential dependence curves of NIR fluorescence intensity on the pumping power
Summary
The increasing demand for solar energy, due to its green and inexhaustible advantage, has put how to improve the photovoltaic conversion efficiency of solar cells at the forefront of research [1]. RE3+-Yb3+ (RE = Tb, Ho, and Pr) couple have been demonstrated with optical spectroscopy for NIR DC in various hosts [2, 6, 9] These DC materials are still far from practical application, because the absorption of the sensitizer RE3+ ion arisen from the parity-forbidden 4ƒ-4ƒ transitions are naturally weak in intensity, narrow in bandwidth, and usually give emission in UV-Vis region [11]. Tb4+ ion might be an ideal broadband sensitizer for Yb3+ ion due to its charge transfer (CT) state located at 300nm-600nm [12, 13]. The sensitizer Tb4+ ion could efficiently transfer the absorbed energy to activator Yb3+ ion without any emission in UV-Vis region, which will provide a better NIR DC system for silicon-based solar cells to improve the photovoltaic conversion efficiency
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