Ag₂S quantum dots (QDs) are well‐known near‐infrared fluorophores and have attracted great interest in biomedical labeling and imaging in the past years. However, their photoluminescence efficiency is hard to compete with Cd‐, Pb‐based QDs. The high Ag⁺ mobility in Ag₂S crystal, which causes plenty of cation deficiency and crystal defects, may be responsible mainly for the low photoluminescence quantum yield (PLQY) of Ag₂S QDs. Herein, a cation‐doping strategy is presented via introducing a certain dosage of transition metal Pb²⁺ ions into Ag₂S nanocrystals to mitigate this intrinsic shortcoming. The Pb‐doped Ag₂S QDs (designated as Pb:Ag₂S QDs) present a renovated crystal structure and significantly enhanced optical performance. Moreover, by simply adjusting the levels of Pb doping in the doped nanocrystals, Pb:Ag₂S QDs with bright emission (PLQY up to 30.2%) from 975 to 1242 nm can be prepared without altering the ultrasmall particle size (≈2.7–2.8 nm). Evidently, this cation‐doping strategy facilitates both the renovation of crystal structure of Ag₂S QDs and modulation of their optical properties.

中文翻译：

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NIR-II窗口中具有均匀粒径和明亮可调荧光的超小Pb：Ag2S量子点

Ag ₂ S量子点（QD）是众所周知的近红外荧光团，并且在过去几年中引起了人们对生物医学标记和成像的极大兴趣。但是，它们的光致发光效率很难与基于Cd，Pb的QD竞争。Ag ₂ S晶体中高的Ag ⁺迁移率会引起大量的阳离子缺乏和晶体缺陷，这可能是造成Ag ₂ S量子点的低光致发光量子产率（PLQY）的主要原因。本文中，通过向Ag ₂ S纳米晶体中引入一定剂量的过渡金属Pb ²⁺离子来减轻这种内在缺陷，提出了一种阳离子掺杂策略。掺杂Pb的Ag ₂ S QD（指定为Pb：Ag ₂S QDs呈现出经过翻新的晶体结构，并显着增强了光学性能。此外，通过简单地调整掺杂纳米晶体中的Pb掺杂水平，可以制备在975至1242 nm范围内具有明亮发射（PLQY高达30.2％）的Pb：Ag ₂ S QD，而无需改变超小粒径（≈2.7-2.8）纳米）。显然，这种阳离子掺杂策略既促进了Ag ₂ S QD的晶体结构的革新，又促进了其光学性能的调节。