Photostable Luminescent Coatings Assembled from Flow-Purified Silicon Nanocrystals: Effects of Size, Packing Order, and Environment

半导体纳米晶体或量子点的独特光学特性非常适合生物医学成像和传感的一系列需求，但迄今为止的工作主要集中在有毒物质，如硒化镉。相比之下，硅是一种丰富的无毒元素，可以很容易地在非热等离子体中合成发光纳米晶体。像所有的量子点一样，硅纳米晶体的光致发光稳定性有限。由于初步数据表明纳米颗粒的堆积与整体光稳定性之间存在明确的联系，我们将进行一项结合实验和计算的研究，研究颗粒尺寸分布、颗粒堆积顺序和局部环境对由纯化硅量子点组装的薄膜和团簇的光稳定性的影响。等离子体合成的纳米晶体将(i)使用不同长度的配体分散在有机溶剂中，（ii）通过密度梯度超离心以可扩展的方式按大小分离成高度单分散的馏分，以及（iii）通过控制干燥组装成有序的薄膜和簇。通过光学和电子显微镜独立测量微观结构，同时测量随时间变化的光谱响应，将建立堆积密度、晶体顺序、局部环境和光稳定性之间的相关性。为了解释这些实验，我们将把干燥胶体悬浮液中非平衡自组装的数值模拟与量子力学模型结合起来，该模型解释了粒子间相互作用对紧密排列的纳米粒子系综的光物理影响。该项目代表了粒子相互作用对硅量子点光稳定性影响的第一个综合科学研究，它将对许多不同的前沿产生重大影响。光致发光这种引人注目的视觉信号是纳米技术在宏观尺度上的一种特别容易接近的表现，我们将利用这一点来吸引公众，包括来自北达科他州的高中生。我们在指导本科生（包括女性和未被充分代表的少数族裔）方面也有良好的记录，通过具有挑战性的项目最终发表了高影响力的出版物。在这个提案中有相当一部分的初步数据是由大学生收集和分析的。在跨学科研究范围的推动下，PI还开发了一门新的研究生课程，专门用于培养“软硬”领域的博士研究人员。界面，它代表了21世纪纳米技术的典范。最后，所获得的知识的潜在技术影响是非常广泛的，从高效的固态照明和溶液处理光伏到光纤温度计和用于活细胞诊断的稳定无毒荧光团。

1133135PI: HobbieThe unique optical properties of semiconductor nanocrystals, or quantum dots, are well suited to a range of needs in biomedical imaging and sensing, but work so far has focused on toxic materials like cadmium selenide. Silicon, in contrast, is an abundant nontoxic element that can be readily synthesized into luminescent nanocrystals in nonthermal plasmas. Like all quantum dots, silicon nanocrystals have limited photoluminescent stability. Motivated by preliminary data that demonstrate a clear link between nanoparticle packing and ensemble photostability, we will perform a combined experimental and computational study of the influence of particle size distribution, particle packing order, and local environment on the photostability of films and clusters assembled from purified silicon quantum dots. The plasma-synthesized nanocrystals will be (i) dispersed in organic solvents using ligands of varied length, (ii) separated by size in a scalable fashion through density-gradient ultracentrifugation into highly monodisperse fractions, and (iii) assembled into ordered films and clusters through controlled drying. Correlations between packing density, crystalline order, local environment, and photostability will be established by independently measuring the microstructure with optical and electron microscopy while simultaneously measuring the time-dependent spectral response. To interpret these experiments, we will combine numerical simulations of non-equilibrium self-assembly in drying colloidal suspensions with a quantum-mechanical model that accounts for the influence of inter-particle interactions on the photophysics of closely packed nanoparticle ensembles.This project represents the first comprehensive scientific study of the influence of particle interactions on the photostability of silicon quantum dots, and it will have significant impact on a number of diverse fronts. The striking visual signal of photoluminescence is a particularly accessible manifestation of nanotechnology at macroscopic scales, and we will exploit this to engage the public, including high school students from across the state of North Dakota. We also have a strong record of mentoring undergraduates, including women and underrepresented minorities, through challenging projects that culminate in high-impact publications. A significant portion of the preliminary data in this proposal were collected and analyzed by undergraduates. Motivated by the interdisciplinary scope of the research, the PI is also developing a new graduate course specifically designed to train doctoral researchers at the ?soft-hard? interface, which represents a paradigm for nanotechnology in the 21st century. Finally, the potential technological impact of the knowledge gained is tremendously broad, ranging from efficient solid-state lighting and solution-processed photovoltaics to fiber-optic cryothermometers and stable non-toxic fluorophores for live cell diagnostics.