Embedding nanocrystals in glass provides a way to create UV-producing LEDs for biomedical applications. Image credit Los Alamos National Laboratory. |
A
multinational team of scientists has developed a process for creating
glass-based, inorganic light-emitting diodes (LEDs) that produce light
in the ultraviolet range. The work, reported recently in the online Nature Communications, is a step toward biomedical devices with active components made from nanostructured systems.
LEDs
based on solution-processed inorganic nanocrystals have promise for use
in environmental and biomedical diagnostics, because they are cheap to
produce, robust, and chemically stable. But development has been
hampered by the difficulty of achieving ultraviolet emission. In their
paper, Los Alamos National Laboratory’s Sergio Brovelli in collaboration
with the research team lead by Alberto Paleari at the University of
Milano-Bicocca in Italy describe a fabrication process that overcomes
this problem and opens the way for integration in a variety of
applications.
The
world needs light-emitting devices that can be applied in biomedical
diagnostics and medicine, Brovelli said, either as active lab-on-chip
diagnostic platforms or as light sources that can be implanted into the
body to trigger some photochemical reactions. Such devices could, for
example, selectively activate light-sensitive drugs for better medical
treatment or probe for the presence of fluorescent markers in medical
diagnostics. These materials would need to be fabricated cheaply, on a
large scale, and integrated into existing technology.
The
paper describes a new glass-based material, able to emit light in the
ultraviolet spectrum, and be integrated onto silicon chips that are the
principal components of current electronic technologies.
The
new devices are inorganic and combine the chemical inertness and
mechanical stability of glass with the property of electric conductivity
and electroluminescence (i.e. the ability of a material to emit light
in response to the passage of an electric current). As a result, they
can be used in harsh environments, such as for immersion into
physiologic solutions, or by implantation directly into the body. This
was made possible by designing a new synthesis strategy that allows
fabrication of all inorganic LEDs via a wet-chemistry approach, i.e. a
series of simple chemical reactions in a beaker. Importantly, this
approach is scalable to industrial quantities with a very low start-up
cost. Finally, they emit in the ultraviolet region thanks to careful
design of the nanocrystals embedded in the glass.
In
traditional light-emitting diodes, light emission occurs at the sharp
interface between two semiconductors. The oxide-in-oxide design used
here is different, as it allows production of a material that behaves as
an ensemble of semiconductor junctions distributed in the glass. This
new concept is based on a collection of the most advanced strategies in
nanocrystal science, combining the advantages of nanometric materials
consisting of more than one component. In this case the active part of
the device consists of tin dioxide nanocrystals covered with a shell of
tin monoxide embedded in standard glass: by tuning the shell thickness
is it possible to control the electrical response of the whole material.
The
paper was produced with the financial support of Cariplo Foundation,
Italy, under Project 20060656, the Russian Federation under grant
11.G34.31.0027, the Silvio Tronchetti Provera Foundation, and Los Alamos
National Laboratory’s Directed Research and Development Program.
Fully inorganic oxide-in-oxide ultraviolet nanocrystal light emitting devices
