OP: Establishing the Crystallochemical Principles Governing Energy-Transfer Processes in Upconversion Nanocrystals

Wayne State University, Detroit MI

Investigators

Abstract

Non-technical description: There is a strong need for bright and multicolor optical probes for biophotonic and photonic applications in fields such as health care (imaging and sensing), energy efficient management (solid-state lighting, photovoltaics, and displays), and defense (solid-state lasers). Upconversion nanocrystals, which convert infrared into visible light, possess unique properties that make them highly desirable optical probes. However, for most of those crystals their implementation has been limited by their low brightness and reduced color tunability. This project focuses on establishing relationships between the chemical composition, atomic structure, and luminescence of upconversion nanocrystals with a view towards designing bright and color-tunable emitters. The project takes advantage of the versatility of a series of nanocrystals whose composition and atomic structure can be finely controlled, and is expected to expand the library of bright and multicolor upconverters, while also generating fundamental knowledge of light-matter interactions at the nanoscale. The project provides new opportunities to contribute to workforce development at both graduate and undergraduate levels. Graduate students are trained in the synthesis and advanced characterization of luminescent nanomaterials. Educational activities are developed to integrate scientific research into undergraduate education through Wayne State University's Nanoengineering Undergraduate Certificate Program. Technical description: Upconversion nanocrystals offer several potential advantages over molecular downconversion fluorophores traditionally employed in biophotonic applications such as optical imaging and sensing. However, their implementation as optical probes has been limited by their low efficiency and lack of full-spectrum color tunability. An ongoing challenge in the field of upconverting nanocrystals is the rational design of efficient and color-tunable emitters via manipulation of the chemical composition and crystal structure. This project utilizes a series of chemically flexible nanomaterials to enable compositional control of structural features directly involved in energy-transfer processes relevant to light upconversion. The goal is to establish a series of crystallochemical principles that create the basis for the rational design of upconverting nanocrystals with optimized energy-transfer pathways through a systematic analysis of composition-structure-luminescence relationships. This project involves solution-phase synthesis of colloidal nanocrystals with controlled chemical composition and size, evaluation of their crystal structure using a combination of multiple spectroscopic techniques (X-ray diffraction, X-ray total scattering, and X-ray absorption), and thorough study of their light upconversion properties using spectrofluorometry (steady-state and time-dependent).