[论文解读] Yb3+ speciation and energy-transfer dynamics in quantum-cutting Yb3+-doped CsPbCl3 perovskite nanocrystals and single crystals

Joo Yeon D. Roh, Matthew D. Smith+5 more|arXiv (Cornell University)|Oct 6, 2020

Perovskite Materials and Applications被引用 7

一句话总结

本研究探究了量子切割Yb3+:CsPbCl3钙钛矿纳米晶体和单晶中Yb3+的物种形态及其能量转移动力学，揭示了量子切割是该材料的本征性质。时间分辨光致发光证实，存在一个关键的皮秒级中间态，介导能量转移，其室温下的衰减速率约为7 ns，解释了接近200%的高光致发光量子产率。

ABSTRACT

Yb3+-doped inorganic metal-halide perovskites (Yb3+:CsPbX3, X = Cl, Br) have recently been discovered to display highly efficient quantum cutting, in which the energy from individual blue or UV photons absorbed by the material is re-emitted in the form of pairs of near-infrared photons by Yb3+ dopants. Experimental photoluminescence quantum yields approaching 200{%} have been reported. As the first quantum-cutting materials that combine such high photoluminescence quantum yields with strong, broadband absorption in the visible, these materials offer unique opportunities for enhancing the efficiencies of solar technologies. Little is known about the fundamental origins of this quantum cutting, however. Here, we describe variable-temperature and time-resolved photoluminescence studies of Yb3+:CsPbCl3 in two disparate forms - colloidal nanocrystals and macroscopic single crystals. Both forms show very similar spectroscopic properties, demonstrating that quantum cutting is an intrinsic property of the Yb3+:CsPbX3 composition itself. Diverse Yb3+ speciation is observed in both forms by low-temperature photoluminescence spectroscopy, but remarkably, quantum cutting is dominated by the same specific Yb3+ species in both cases. Time-resolved photoluminescence measurements provide direct evidence of the previously hypothesized intermediate state in the quantum-cutting mechanism. This intermediate state mediates relaxation from the photogenerated excited state of the perovskite to the emissive excited state of Yb3+, and hence is of critical mechanistic importance. At room temperature, this intermediate state is populated within a few picoseconds and has a decay time of only ~ 7 ns in both nanocrystalline and single-crystal Yb3+:CsPbCl3. The mechanistic implications of these observations are discussed.

研究动机与目标

• 理解Yb3+:CsPbCl3钙钛矿中高效量子切割的根本起源。
• 确定量子切割行为在纳米晶体与单晶之间是否存在差异。
• 识别在两种形态中负责量子切割的特定Yb3+物种。
• 表征量子切割机理中假设的中间能量转移态。
• 量化Yb3+:CsPbCl3中能量转移与弛豫路径的动力学过程。

提出的方法

• 对Yb3+:CsPbCl3纳米晶体和单晶进行了变温及时间分辨光致发光光谱测量。
• 采用低温光致发光以分辨不同的Yb3+物种及其光谱特征。
• 测量皮秒级动力学，以识别并表征能量转移路径中的中间态。
• 比较胶体纳米晶体与宏观单晶的光谱性质，评估结构影响。
• 利用衰减速率分析确定两种形态中中间态的寿命。
• 将能量转移动力学与光致发光量子产率相关联，以验证量子切割机理。

实验结果

研究问题

• RQ1 Yb3+的物种形态在决定Yb3+:CsPbCl3中量子切割效率方面起什么作用？
• RQ2 Yb3+:CsPbCl3纳米晶体与单晶之间的能量转移动力学有何不同？
• RQ3 量子切割能量转移路径中的中间态的性质及其寿命是什么？
• RQ4 在纳米晶和单晶形态中，哪种特定Yb3+物种主导了量子切割过程？
• RQ5 所观测到的动力学如何解释实验报道的接近200%的光致发光量子产率？

主要发现

• 量子切割是Yb3+:CsPbCl3的本征性质，纳米晶体与单晶表现出几乎相同的光谱行为。
• 低温光致发光揭示了多种Yb3+物种，但量子切割在纳米晶体与单晶中均由同一种特定Yb3+物种主导。
• 时间分辨光致发光为量子切割机理中一个关键中间态的存在提供了直接证据，该中间态在室温下于数皮秒内被占据。
• 该中间态在Yb3+:CsPbCl3纳米晶体和单晶中的衰减速率均约为7 ns。
• 该中间态的存在及其动力学特性解释了接近200%的高光致发光量子产率。
• 能量转移路径通过一个快速的皮秒级弛豫过程，经由中间态到达发射态Yb3+激发态，从而实现高效的量子切割。