In addition to its annual lectures, ChBE hosts a weekly seminar throughout the year with invited lecturers who are prominent in their fields. Unless otherwise noted, all seminars are held on Wednesdays in the Molecular Science and Engineering Building ("M" Building) in G011 (Cherry Logan Emerson Lecture Theater) at 4:00 p.m. Refreshments are served at 3:30 p.m. in the Emerson-Lewis Reception Salon.

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Two approaches to achieve visible light upconversion for environmental application

This talk summarizes our most recent advances in developing antimicrobial/biocidal materials that function through light frequency amplification process called upconversion (UC). The first approach is based on inorganic luminescent materials that can convert visible light into germicidal UVC and have been shown to inactivate microorganisms deposited on dry surface and deter biofilm formation under commercial fluorescent light exposure. Upconversion efficiencies of current phosphor systems are too low for practical antimicrobial/biocidal application, however, and methods of enhancing internal optical efficiency are required for further advancement. Lithium ion doping is a commonly employed, yet sparsely understood option for improving emission intensity in UC phosphors, including the visible-to-UV converting material Y2SiO5:Pr3+.

In this work, for the first time, we have identified and quantified the major mechanisms by which Li+ enhances UC in a phosphor, using crystallographic and spectroscopic techniques in the form of X-ray diffraction, neutron diffraction, photoluminescence spectroscopy, and electron microscopy. Results show that 10 at.% doping with Li+ improves UV emission 9-fold and is attributed to crystallite enlargement, induction of a phase change, and increasing inter-ion separation of the Pr3+ activator. The second UC approach is based on a completely different mechanism of sensitized triplet-triplet annihilation in an organic matrix.

Moldable rubbery urethane materials generated from their corresponding polymeric precursors produce high efficiency regenerative green-to-blue upconverting solids when impregnated with benchmark palladium(II) octaethylporphyrin (PdOEP) sensitizers and 9,10-diphenylanthracene (DPA) acceptor/annihilator molecules. The cured soft materials promote sufficient diffusion at room temperature to support the sequential bimolecular reactions necessary for both triplet sensitization and triplet-triplet annihilation occurring between the precisely doped chromophores. UC quantum yields measured in linear incident light power dependence region exceeded 20%, over an order-of-magnitude greater than all previously investigated solids. These materials are intended as host materials enabling sub-bandgap sensitization of semiconductor photocatalysts such as WO3 to enhance visible light susceptibility in environmental decontamination application.