Antolinez Felipe V, Rabouw Freddy T, Rossinelli Aurelio A, Keitel Robert C, Cocina Ario, Becker Michael A, Norris David J
Optical Materials Engineering Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
IBM Research Europe - Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland.
Nano Lett. 2020 Aug 12;20(8):5814-5820. doi: 10.1021/acs.nanolett.0c01707. Epub 2020 Jul 7.
Colloidal nanoplatelets (NPLs) are atomically flat, quasi-two-dimensional particles of a semiconductor. Despite intense interest in their optical properties, several observations concerning the emission of CdSe NPLs remain puzzling. While their ensemble photoluminescence spectrum consists of a single narrow peak at room temperature, two distinct emission features appear at temperatures below ∼160 K. Several competing explanations for the origin of this two-color emission have been proposed. Here, we present temperature- and time-dependent experiments demonstrating that the two emission colors are due to two subpopulations of uncharged and charged NPLs. We study dilute films of isolated NPLs, thus excluding any explanation relying on collective effects due to NPL stacking. Temperature-dependent measurements explain that trion emission from charged NPLs is bright at cryogenic temperatures, while temperature activation of nonradiative Auger recombination quenches the trion emission above 160 K. Our findings clarify many of the questions surrounding the photoluminescence of CdSe NPLs.
胶体纳米片（NPLs）是原子级平整的准二维半导体颗粒。尽管人们对其光学性质有着浓厚的兴趣，但关于CdSe NPLs发射的一些观察结果仍然令人困惑。虽然它们在室温下的整体光致发光光谱由一个单一的窄峰组成，但在低于约160 K的温度下会出现两个不同的发射特征。已经提出了几种关于这种双色发射起源的相互竞争的解释。在这里，我们展示了温度和时间相关的实验，证明这两种发射颜色是由于不带电和带电NPLs的两个亚群造成的。我们研究了孤立NPLs的稀薄膜，从而排除了任何依赖于NPL堆叠的集体效应的解释。温度相关的测量结果表明，带电NPLs的三重态激子发射在低温下很亮，而非辐射俄歇复合的温度激活会在160 K以上淬灭三重态激子发射。我们的发现澄清了围绕CdSe NPLs光致发光的许多问题。
