mize the device for best performance,”
Next, he plans to develop multiscale
simulation on organic solar cells based on
the correct understanding of the nanoscale
morphology of the bulk heterojunctions.
Such simulation will help scientists find
the optimal materials, design and processing conditions that could lead to the best
performance for the device.
The research was funded by the National Science Foundation.
These organic solar cells are
made from bulk heterojunctions
formed from blending donor and
acceptor. Courtesy of Guangyong Li, University of Pittsburgh.
Material glows in NIR for two weeks
ATHENS, Ga. – Move over, cheesy glow-in-the-dark plastic toys that take forever
to “charge up” with light and that fade to
black in a blink. A new material can emit a
near-infrared glow for two weeks after a
single minute of exposure to sunlight, or
even fluorescent lights – and its creators
envision applications more important than
playthings. It could revolutionize medical
diagnostics, supply a secret source of illumination for law enforcement and military
agencies, or provide the foundation for
highly efficient solar cells.
While visible-light emitters are commonplace, there has been little success in
creating materials that emit NIR light –
until now. The new material from the University of Georgia is composed of trivalent
chromium ion, a well-known emitter of
NIR light. When exposed to light, its electrons at ground state quickly move to a
higher-energy state. As they return to the
ground state, energy is released as NIR
light. Typically the period of light emission is on the order of a few milliseconds.
The new material uses a matrix of zinc
and gallogermanate to host the trivalent
chromium ions. Its chemical structure creates a labyrinth of “traps” that capture excitation energy and store it for an extended
period. As the stored energy is thermally
released back to the chromium ions at
room temperature, the compound persistently emits NIR light over a period of up
to 360 hours.
“We have successfully discovered a se-
ries of trivalent chromium ion-doped gal-
lates that have extraordinary capabilities in
excitation energy absorption, storage, NIR
light conversion and very long NIR light
afterglow,” said Zhengwei Pan, associate
professor of physics and engineering at
Franklin College of Arts and Sciences; he
is also on the engineering faculty. “We ex-
pect that this work will not only stimulate
the research in persistent luminescent ma-
terials, but also several important areas for
applications including defense and foren-
sics, solar energy utilization and in vivo
He explained that the material could be
fabricated into nanoparticles that bind to
cancer cells, for example, so doctors could
visualize small metastases that otherwise
might go undetected. For military and law
enforcement, the material could be fash-
ioned into ceramic discs that are visible
only to those wearing night-vision gog-
gles. It could also provide the foundation
for highly efficient solar cells, Pan said.
Zhengwei Pan, associate professor of physics and engineering, and postdoctoral researcher Feng Liu stand
in a darkened room, using only their recently invented ceramic discs, which emit NIR light, as a source of
illumination. Their phosphorescent material was mixed into the paint used to create the University of Georgia
logo behind them. There is no other source of illumination in the room; without the aid of a night-vision device, the image would be completely dark. At right, 5 g of NIR persistent powder glowing
in a glass vial. Images courtesy of Pan and Liu.