Hi,
Vlad Tarabara is hosting a prominent speaker on Friday who
will talk on efficient up-conversion and its applications.
The notice is below,
Phil
Environmental
Engineering seminar
All students, faculty, and staff are welcome.
Friday, September 14, 2012
1:30pm – 2:30pm
3540 Engineering Building
Dr. Jaehong Kim
Georgia Power Distinguished Associate Professor
School of Civil and Environmental Engineering
Georgia Institute of Technology
Two Approaches to Achieve Visible Light Upconversion for
Environmental Application
Abstract
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 TiO2 to
enhance visible light susceptibility in environmental
decontamination application.
Accommodations for persons with disabilities may be requested by
contacting Mrs. Lori Larner ([log in to unmask]).
--
Volodymyr V. Tarabara, PhD
Associate Professor, Environmental Engineering
Associate Director, Environmental Science and Policy Program
Michigan State University
www.egr.msu.edu/~tarabara