Colloidal semiconductor nanocrystals (NCs) have been recognized as promising solution-processable gain media; however, the lasers with state-of-the-art performance exclusively originate from the cadmium- and lead-based NCs. Herein, we for the first time unravel that high-quality heavy-metal-free ZnSe/ZnS NCs show superior optical gain and lasing performance when the sizes exceed the quantum confinement regime. Corroborated by comprehensive transient spectroscopy, we reveal that the optical gain in large ZnSe/ZnS NCs originates from the novel Coulomb-correlated electron–hole plasma (C-EHP) instead of high-order multi-exciton recombination. Thanks to the formation of a four-level system and the suppression of Auger recombination, the C-EHP renders low gain threshold (9.4 μJ/cm2), high gain coefficient (>6500 cm−1), and long gain lifetime (∼4 ns). Such desirable gain properties compete well with those of classic CdSe NCs and enable the construction of a high-performance laser device. This work represents significant progress toward the development of solution-processable non-heavy-metal nanocrystal lasers.

中文翻译：

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库仑相关电子空穴等离子体诱导硒化锌胶体纳米晶体具有优异的光学增益

胶体半导体纳米晶体（NC）已被认为是有前途的可溶液加工的增益介质；然而，具有最先进性能的激光器完全源自镉基和铅基数控系统。在此，我们首次揭示了当尺寸超过量子限制范围时，高质量不含重金属的 ZnSe/ZnS NC 表现出优异的光学增益和激光性能。通过综合瞬态光谱证实，我们揭示了大型 ZnSe/ZnS NC 中的光学增益源自新型库仑相关电子空穴等离子体（C-EHP），而不是高阶多激子复合。由于四能级系统的形成和俄歇复合的抑制，C-EHP具有低增益阈值（9.4 μJ/cm2）、高增益系数（>6500 cm−1）和长增益寿命（∼ 4纳秒）。这种理想的增益特性可与经典 CdSe NC 相媲美，并可构建高性能激光设备。这项工作代表了可溶液加工的非重金属纳米晶体激光器的开发取得了重大进展。