Understanding Thermal Energy Scavenging in All-Inorganic Perovskite Nanocrystals

非技术概述：工业革命是由热机推动的，热机通过将热能(热能或高温)转化为机械能来做功。最近，通过将热转化为光来工作的热机有几个优点，类似于传统发动机使用液体或气体(如蒸汽)的方式。然而，已知的能够有效地将热能转化为光能的光学材料很少，部分原因是热降低了它们的光学性能。该项目将在纳米尺度上制备具有精确结构和化学性质的新型材料，以实现热能和光能之间的有效转换。研究小组将研究增加这些材料中的热能如何也会异常地导致它们发出的光能增加。这种现象最终可以导致没有移动部件的更高效的热机，更好的太阳能电池，或者不需要压缩气体或机械部件的新的制冷方法。该项目将支持在PI实验室工作的研究生和本科生，以及开发用于教授大型新生化学课程的新课程和技术工具。主要研究人员将提炼大流行期间开发的一些最好的创新，并利用这些创新来过渡到课堂教学。技术摘要：这个项目将研究通过单光子光学上转换来清除热能，也称为反斯托克斯光致发光。当加热的光致发光材料在亚禁带激发过程中发射带边光子，同时温度降低时，会产生上转换。无机卤化铅钙钛矿纳米晶是一种高效的单光子上转换材料体系，但其机理的基本细节尚不清楚，阻碍了进一步发展的合理策略。PI团队进行的光谱研究将阐明光学上转换的明确机制，并概述定义吸收截面、带宽、温度响应和效率的基本限制的结构-性质关系。研究小组将在纳米晶体合成过程中改变成分和形态。利用高分辨率电子显微镜和粉末X射线衍射仪将跟踪晶体相、形状和表面积与体积比等结构参数。同时，该团队将进行光致发光激发光谱和光致发光寿命研究。这些实验将量化对能隙以上或能隙以下激发波长、功率密度和纳米晶体温度的依赖关系，以确定介导振动和电子激发相互转换的独特状态，同时保持纳米晶体固有的、接近理想的发光效率。主要目标是了解无机卤化铅钙钛矿纳米晶体的热能清除特性，以创造有助于热能到光能转换、光学上转换和光驱动制冷的发光材料。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智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY:The industrial revolution was enabled by heat engines that perform work by converting thermal energy (heat or high temperature) to mechanical energy. Recently, several advantages have been theorized for heat engines that do work by converting heat into light, similar to how traditional engines use fluids or gases such as steam. However, there are very few known optical materials that can efficiently convert heat to optical energy, in part because heat degrades their optical performance. This project will prepare new classes of materials with precise structural and chemical properties on the nanoscale to allow for efficient conversion between thermal and light energy. The research team will examine how increasing the thermal energy in these materials can also result, unusually, in an increase of the energy of light that they emit. This phenomenon can ultimately lead to significantly more efficient heat engines with no moving parts, better solar cells, or new methods of refrigeration that do not require compressed gasses or mechanical components. The project will support graduate and undergraduate research students working in the PI’s laboratory as well as the development of novel curricula and technological tools for teaching large-format freshman chemistry courses. The primary investigator will refine some of the best innovations developed during the pandemic and take advantage of these for the transition back to classroom instruction.TECHNICAL SUMMARY:This project will study thermal energy scavenging by one-photon optical upconversion, also known as anti-Stokes photoluminescence. Upconversion results when heated photoluminescent materials emit band-edge photons during subgap excitation, while simultaneously decreasing in temperature. Inorganic lead halide perovskite nanocrystals are a champion materials system for efficient one-photon upconversion, but fundamental details of the mechanism are unknown, impeding rational strategies for further development. Spectroscopic studies conducted by the PI’s team will elucidate a clear mechanism for optical up-conversion, as well as outline the structure-property relationships that define the absorption cross section, bandwidth, temperature response, and the fundamental limits on efficiency. The research team will vary composition and morphology during nanocrystal synthesis. Structural parameters such as crystal phase, shape, and surface-to-volume ratio will be tracked using high resolution transmission electron microscopy, and powder X-ray diffractometry. In parallel, the team will perform photoluminescence excitation spectroscopy and photoluminescence lifetime studies. These experiments will quantify the dependence on above-gap or below-gap excitation wavelength, power density, and nanocrystal temperature to identify the unique states that mediate the interconversion of vibrational and electronic excitations, while preserving the intrinsic, near-ideal luminescence efficiency of the nanocrystals. The overarching goal is to understand the thermal energy scavenging properties of inorganic lead halide perovskite nanocrystals to create luminescent materials that can aid thermal-to-optical energy conversion, optical up-conversion, and optically driven refrigeration.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.