Lead halide perovskite quantum dots (PQDs) have shown remarkable single‐photon upconversion photoluminescence (SPUC‐PL) bringing them a brilliant perspective as the active media for biological imaging, optiag, and upconversion photovoltaics. However, the mechanism of SPUC in PQDs is still in dispute, and the specific strategy for optimizing PQDs toward a higher SPUC performance has yet to be established, which impedes the application of PQDs‐based SPUC‐PL in practice. In this work it is revealed that the PL quantum yield is declined by surface trap states, while the SPUC efficiency is promoted by Urbach tail states. These two types of intragap states can be chemically manipulated by engineering the surface ligand and the growth kinetics of perovskite nanocrystals, bringing on the improvement of light emission efficiency and the promotion of subgap low‐energy photon absorption, respectively. As a proof of concept, utilizing the synergistic effect of the proposed chemical manipulation method, the SPUC‐PL efficiency of PQDs is boosted by more than 40%, which gives rise to a spectral window of optical refrigeration gain as broad as ≈130 meV.

中文翻译：

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通过间隙内态调控实现钙钛矿量子点的高效单光子上转换光致发光

卤化铅钙钛矿量子点（PQD）表现出卓越的单光子上转换光致发光（SPUC-PL），为它们作为生物成像、光学和上转换光伏的活性介质带来了广阔的前景。然而，SPUC在PQDs中的作用机制仍存在争议，并且尚未建立优化PQDs以获得更高SPUC性能的具体策略，这阻碍了基于PQDs的SPUC-PL在实践中的应用。这项工作揭示了表面陷阱态会降低 PL 量子产率，而 Urbach 尾态会提高 SPUC 效率。这两种类型的带隙内态可以通过设计表面配体和钙钛矿纳米晶体的生长动力学来进行化学操纵，从而分别提高发光效率和促进亚带隙低能光子吸收。作为概念验证，利用所提出的化学操作方法的协同效应，PQD 的 SPUC-PL 效率提高了 40% 以上，从而产生了宽达 ≈130 meV 的光学制冷增益光谱窗口。