Perovskite-Modified LEDs Reveal Rot in Fruit and Veg Before It Is Visible
A team of researchers has developed new LEDs which emit light
simultaneously in two different wavelength ranges, for a simpler and
more comprehensive way to monitor the freshness of fruit and vegetables.
As the team write in the journal Angewandte Chemie, modifying
the LEDs with perovskite materials causes them to emit in both the
near-infrared range and the visible range, a significant development in
the contact-free monitoring of food.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Perovskite crystals are able to capture and convert light. Being
simple to produce and highly efficient, perovskites are already used in
solar cells but are also being intensively researched for suitability in
other technologies. Angshuman Nag and his team at the Indian Institute
of Science Education and Research (IISER) in Pune, India, are now
proposing a perovskite application in LED technology that could simplify
the quality control of fresh fruit and vegetables.
Without light converters, LEDs would emit light in rather narrow
light bands. To cover the whole range of white light produced by the
sun, the diodes in “phosphor-converted” (pc) LEDs are coated with
luminescent substances. Nag and his team have used a double emission
coating with the purpose to produce pc-LEDs that emit both white
(“normal”) light and also a strong band in the near-infrared range
(NIR).
To make the dual-emission pc-LED, they applied a double perovskite
doped with bismuth and chromium. Part of the bismuth component emits
warm white light and another part transfers energy to the chromium
component, de-exciting it and causing an additional emission in the NIR
range, the researchers found out.
NIR is already used in the food industry to examine freshness in
fruit and vegetables. Nag and PhD student Sajid Saikia, first author of
the paper, explain their idea: "Food contains water, which absorbs the
broad near-infrared emission at around 1000 nm. The more water that is
present [due to rotting], the greater the absorption of near-infrared
radiation, yielding darker contrast in an image taken under
near-infrared radiation. This easy, non-invasive imaging process can
estimate the water content in different parts of food, assessing its
freshness."
Using these modified pc-LEDs to examine apples or strawberries, the
team observed dark spots that were not visible in standard camera
images. Illuminating the food with both white and NIR light revealed
normal coloring that could be seen by the naked eye, as well as those
parts which were starting to rot, but not yet visibly so.
Saikia and Nag envision a compact device for simultaneous visual and
NIR food inspection, although the two detectors, one for visible light
and one for NIR light, could make such an instrument costly for common
applications. On the other hand, the researchers emphasize that the pc
LEDs are easy to produce without any chemical waste or solvents and
short-term costs could be more than recovered by the long service life
and scalability of this novel dual-emitting pc-LED device.
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About the Author
Angshuman Nag is an
Associate Professor of Chemistry at IISER Pune, India. His group
develops novel semiconductors with favorable optoelectronic properties
such as defect-free nanocrystals, lead-free metal halide perovskites,
semiconductors with luminescent, plasmonic, and magnetic properties, and
surface-engineered nanocrystals.
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