Understanding Thermal Energy Scavenging in All-Inorganic Perovskite Nanocrystals

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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.