Infrared Luminescence and Optical Characterization
My research interests focus on exploring the optical properties of
materials with an eye toward understanding novel luminescent materials
in terms of the radiative and non-radiative interactions that affect
luminescent efficiencies. My graduate work focused on understanding the
nature of the luminescent center in Chromium doped crystals that
exhibited strong broad band emission in the near-infrared. These
materails have sinced been commercialized as solid state tunable lasers.
Common near infrared emission centers in solid state hosts include Rare
Earth atoms (Erbium, Ytterbium, Thulium, Holmium, and Neodymium) and
transitions metal ions (Cr4+ and Ti3+). My
research work has explored materials that are relatively easy to make
that are doped with one or more of these atoms to explore the
efficiency of emission from the optically active atoms.
Endohedral fullerenes are a class of molecules consisting of one or
more metal atoms/ions surrounded by a fullerene molecule. The metals
are incorporated inside the fullerene molecules during the fabrication
process by doping the graphite rods with a rare earth oxide (RE2O3).
The fabrication of fullerenes is accomplished using a water cooled
reactor in which we can control the He pressure during the high
current discharge between graphite rods to produce the fullerenes. A
welder provides a current of about 150 Amps between two closely spaced
graphite rods. The arc causes the atoms in the rods to be vaporized
into an explanding cloud that is moderated by the residual He gas in
the chamber. During the expansion of these atoms, some of the carbon
atoms from small sheets that eventually wrap into fullerenes primarily.
However, when the RE atoms are also present, of the fullerenes form by
wrapping around the RE atom or atoms to create the endohedral
fullerenes. My groups first results on these studies were the
observation of emission from Er2@C82.
More recently we have been exploring the possibility of observing emission from Er atoms wrapped in C60.
The challenge here is to mesure the weak emission from the small
endohedralfullerenes that are not produced in large quantities in our
reactor. In addition, it is not clear how stable these endohedral
fullerenes are after production and what happens to them if they
With the ubiquitous use of glass fibers for high-speed optical
communication, the desire for cheaper glass materials with optimized
optical properties drives research in alternate ways of making these
fibers. Sol-gel glass is produced in a room temperature chemical
reaction that may circumvent some of the doping problems associated
with solubility of impurity atoms in molten glass. In addition, because
high temperatures are not required, temperature sensitive molecular
systems can be doped into sol-gel glasses opening up new opportunities
to adjust the emission and absorptions properties of the glass.
Much of this work was part of a collaboration with colleagues Dan Boye
(Davidson College) and Ann Silversmith (Hamilton College). We first
explored the emission efficiency question using Terbium as the primary
probe atom. Our work resulted in several publicaitons elucidating the
problem of RE ion clustering during the sol-gel reaction and describing
the effects of energy transfer resulting from this clustering behavior.
More recent work has focused on ways to insulate the RE ions from water
vapor that diffuses into sol-gel glasses through the pores that
remain after the formation of the silicate chains forming the glass.
Our work has explored the simple chelating agent Dipicolinic Acid (DPA)
. Our most recent work has shown that we can obtain emission from Er
doped DPA and have measured the lifetime which if sub microsecond.
I have explored this method of crystal formation with a couple of
students over the years to explore new ways of fabricating materials in
which we can modify the optical properties by doping impurities. So far
we have made YAG micro crystals using this method. I may push forward
with exploring other crystal hosts with some promise of being a novel
optical material. The technique involves mixing together the base
elements of teh crystal, dopant atoms, a fuel and an oxidizing agent.
The liquid mixture is placed in a crucible that is subsequently
heated to the combustion temperature of the fuel and the rapid heating
provides the thermal energy for nano crystal formation. My work
in this area remains unpublished.