The impact of Yb concentration on multiband upconversion in a single NaYF:Yb/Er microcrystal determined nanosecond time-resolved spectroscopy

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2022-11, Vol.1 (42), p.15897-1595
• Main Authors: Huang, Hanchang, Yuan, Maohui, Xing, Zhongyang, Cui, Wenda, Yu, Tongcheng, Hu, Shuai, Zhao, Guomin, Guo, Chuan, Han, Kai
• Format: Article
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc03013f

In lanthanide-sensitized upconversion (UC) nanomaterials, the typical sensitizer Yb 3+ can significantly modulate the codoped activator (such as Er 3+ ions) to generate multiband transitions. However, the kinetics of these multiband emissions affected by the Yb 3+ concentration remains unclear. In this work, we employ nanosecond time-resolved spectroscopy to investigate a single optically trapped NaYF 4 :Yb/Er microcrystal (MC) doped with different Yb 3+ concentrations. Interestingly, high doping Yb 3+ ions shorten the UC response time by a factor of 10 (from ∼1 μs to ∼100 ns) compared to low doping Yb 3+ . Meanwhile, 430 nm light ( 4 G 7/2 → 4 I 11/2 ) emitted before 654 nm ( 4 F 9/2 → 4 I 15/2 ) with Yb 3+ dramatically increasing (opposite to the normal low Yb 3+ doping cases), representing a new four-photon pathway ( 4 I 15/2 → 4 I 11/2 → 4 F 7/2 → 2 H 11/2 → 4 S 3/2 → 2 G 7/2 → 4 G 11/2 → 2 H 9/2 → 2 D 5/2 → 4 G 7/2 ). Furthermore, we observed a broad range of time-dependent emission color, changing from being initially green over near-white to red. Particularly, the red emission is dominated in the decay process, yielding insight into the fundamental multiband UC kinetics. The result shows that varying the Yb 3+ doping concentration provides a way to control the energy flow between the energy levels of Er 3+ ions, which can modulate the response time and color evolution of UC on Yb/Er doped materials. This can direct the prospective development of fast-response optoelectronic devices, photocatalysis, and UC displays in the future. In lanthanide-sensitized upconversion (UC) nanomaterials, the typical sensitizer Yb 3+ can significantly modulate the codoped activator (such as Er 3+ ions) to generate multiband transitions.