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HomeWorldDye-based Device Sees The Invisible

Dye-based Device Sees The Invisible


Devices that can see shortwave infrared light, which is
invisible to the naked eye, could soon become cheaper and
more accessible to a broader consumer base.

Tsukuba,
Japan, Apr 16, 2021 – (ACN Newswire) – Scientists in Europe
have designed an organic dye-based device that can see light
waves in the shortwave infrared (SWIR) range. The device is
easy to make using cheap materials, and is stable at high
temperatures. The findings, published in the journal Science
and Technology of Advanced Materials, could lead to more
widespread use of inexpensive consumer SWIR imaging and
sensing devices.

In
the upconversion device, shortwave infrared (SWIR) light
with wavelengths beyond 1,000 nm is absorbed by the
squaraine dye in the photodetector (PD), producing
electrical charges. Charges flow into the organic
light-emitting diode (OLED), where they recombine under the
emission of visible light. This way, SWIR light, which
cannot be detected by the human eye, is converted into
visible light.

The human eye can
only detect a very narrow segment of the electromagnetic
spectrum, from around 400 to 700 nanometers. The SWIR
region, on the other hand, extends from 1,000 to 2,500
nanometers. Specially designed cameras can take images of
objects that reflect waves in the SWIR region. They are used
for improving night vision, in airborne remote sensing, and
deep tissue imaging. The cameras also help assess the
composition and quality of silicon wafers, building
structures and even food produce.

“These cameras are
typically difficult to manufacture and are quite expensive,
as they are made of inorganic semiconductor photodiode
arrays interconnected with read-out integrated circuitry,”
says Roland Hany of the Swiss Federal Laboratories for
Materials Science and Technology.

Hany worked with
colleagues in Switzerland and Italy to design an organic
dye-based ‘SWIR upconversion device’ that efficiently
converts shortwave infrared light to visible
light.

The device uses organic (materials made with
carbon) components: a squaraine dye-coated flexible
substrate combined with a fluorescent organic light-emitting
diode (OLED). When the dye absorbs SWIR waves, an electric
current is generated and directly converted into a visible
image by the OLED.

The team had to play with the
molecular composition of several squaraine dyes to get them
to absorb specific wavelengths. Ultimately, they synthesized
squaraine dyes that absorb SWIR light beyond 1,200
nanometers and remained stable up to 200 degrees Celsius.
The finished dye-based device performed stably for several
weeks under normal laboratory conditions.

“All-organic
upconverters could lead to applications that can’t be
realized with current technology. For example, invisible
night vision devices can be directly integrated into car
windscreens without affecting the visual field,” explains
Hany.

The team is now working on shifting the dye’s
absorption further into the SWIR range. They are also using
machine learning techniques to find new dye molecules
capable of sensing SWIR waves. Finally, the team aims to
improve device stability and sensitivity.

About
Science and Technology of Advanced Materials
Journal

Open access journal STAM publishes outstanding
research articles across all aspects of materials science,
including functional and structural materials, theoretical
analyses, and properties of
materials.

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