Department of Chemistry, The Pennsylvania University, University Park, Pennsylvania 16802, United States.
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States.
J Phys Chem Lett. 2021 Aug 12;12(31):7531-7536. doi: 10.1021/acs.jpclett.1c02100. Epub 2021 Aug 4.
Near-infrared photoluminescence of a series of three gold monolayer protected clusters (MPCs) with volumes spanning 50-200 Å was studied by using variable-temperature photoluminescence (VT-PL) spectroscopy. The three MPCs, which included Au(SCH)-diglyme, Au(SCH), and Au(SCH), all exhibited temperature-dependent intensities that reflected a few-millielectronvolt energy gap that separated bright emissive and dark nonradiative electronic states. All clusters showed increased PL intensities upon raising the sample temperature from 4.5 K to a cluster-specific value, upon which increased sample temperature resulted in emission quenching. The increased PL in the low-temperature range is attributed to thermally activated carrier transfer from dark to bright states. The quenching at elevated temperatures is attributed to nonradiative vibrational relaxation through Au-Au stretching of the MPCs metal core. Importantly, the results show evidence of a common and size scalable metal-centered intraband PL mechanism that is general for ultrasmall metal nanoclusters, which are expected to show nonscalable optical properties.
采用变温光致发光（VT-PL）光谱法研究了一系列三个金单层保护簇（MPC）的近红外光致发光，这些簇的体积跨越了 50-200 Å。这三种 MPC 包括 Au(SCH)-diglyme、Au(SCH) 和 Au(SCH)，它们都表现出与温度相关的强度，反映了几个毫电子伏特的能隙，将明亮的发射和暗的非辐射电子态分开。所有的簇在将样品温度从 4.5 K 升高到特定于簇的温度时，都会表现出 PL 强度的增加，而升高的样品温度会导致发射猝灭。低温范围内 PL 的增加归因于热激活的载流子从暗态到亮态的转移。在高温下猝灭归因于 MPC 金属核的 Au-Au 伸缩的非辐射振动弛豫。重要的是，结果表明存在一种常见的、尺寸可扩展的金属中心内带 PL 机制，该机制对于超小金属纳米簇是通用的，预计它们会表现出不可扩展的光学性质。
