Collaborative Research: Optical Transitions in Metallic Nanoclusters at High Pressure

本研究项目致力于纳米材料的创新，这些纳米材料在生物医学治疗、传感和催化方面非常有用。由少于200个金属原子组成的纳米团簇由于其在近红外光下的发光，生物相容性和超小尺寸而受到关注。这些纳米团簇的结构与光学性质之间的关系尚不清楚，这阻碍了设计具有优化性能的纳米团簇。该程序使用压力来修改纳米团簇的结构，以了解负责光吸收和发光的电子跃迁，以及纳米团簇在外部刺激下的稳定性。这项研究与我们的教育计划密切相关，通过培训博士后和研究生，支持K-12和大学科学技术水平的代表性不足的群体，以及支持社区的科学教师。此外，在这个项目中，解释力学对光学行为影响的模块将被纳入本科课程。技术概述：本研究涉及利用金刚石砧细胞技术施加高压，并利用光学测量（吸收和发射）来研究激发态，表征由金或银加配体组成的原子精确团簇的性质。实验将使用电子结构理论建模，包括基态计算来确定结构，激发态研究来确定光学性质，并包括基于二次线性响应理论和域分离密度泛函理论的方法开发。该研究旨在确定光学性质，如等离子体到激子的跃迁，以及随压力增加的发光效率；这两个属性对于在实际应用程序中使用集群都很重要。该研究包括三个研究目标：(1)研究团簇材料在压力下广泛吸收和近红外发光的能量转移，(2)确定纳米团簇异常多次发射的来源，(3)研究2-3 nm纳米团簇从等离子态到激子态转变的特征。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis research program contributes to innovations in nanomaterials that are useful in biomedical therapies, sensing, and catalysis. Nanoclusters that consist of fewer than ~200 metallic atoms are of interest due to their luminescence in near-infrared light, bio-compatibility and ultra-small size. The relationship between the structure and optical properties of these nanoclusters remains unclear, which prevents the design of nanoclusters with optimized performance. This program uses pressure to modify the structure of nanoclusters, in order to learn about the electronic transitions that are responsible for light absorption and luminescence, as well as the stability of nanoclusters under external stimulus. This research is closely tied to our educational plans through the training of postdocs and graduate students, by supporting underrepresented groups at the K-12 and college level in science and technology, and by supporting science teachers in the community. In addition, modules that explain the influence of mechanics on optical behavior will be incorporated into undergraduate courses during this program.TECHNICAL SUMMARYThe proposed research is concerned with characterizing the properties of atomically precise clusters composed of gold or silver plus ligands using diamond anvil cell techniques to apply high pressure, and with optical measurements (both absorption and emission) to study excited states. The experiments will be modeled using electronic structure theory, including ground state calculations to determine structures, and excited state studies to determine optical properties, and including methods development based on second linear response theory and domain-separated density functional theory. The research is aimed at identifying optical properties such as plasmon to exciton transitions, and an increase in luminescence efficiency with increasing pressure; both properties are of interest to using the clusters in practical applications. The research includes three research objectives: (1) study of energy transfer responsible for broad absorption & near-infrared luminescence of the cluster material under pressure, (2) determine the source of anomalous multiple emissions of the nanoclusters, and (3) studies of 2-3 nm nanoclusters to characterize the transition from plasmonic to excitonic states.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.