A multinational team of scientists has developed a process for creating glass-based, inorganic LEDs that produce light in the ultraviolet range. The work 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 inexpensive to produce, robust, and chemically stable. Development has been hampered by the difficulty of achieving ultraviolet emission. Led by Alberto Paleari at the University of Milano-Bicocca in Italy, the team developed a fabrication pro cess that overcomes this problem and opens the way for integration in a variety of applications.

Embedding nanocrystals in glass provides a way to create UV-producing LEDs for biomedical applications. (Los Alamos National Laboratory)
There is a need for LEDs that can be applied in biomedical diagnostics and medicine, either as active, lab-on-a-chip diagnostic platforms, or as light sources that can be implanted into the body to trigger photochemical reactions. Such devices could selectively activate light-sensitive drugs or probe for the presence of fluorescent markers in medical diagnostics.

A new glass-based material, able to emit light in the ultraviolet spectrum, would 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. As a result, they can be used in harsh environments, or implanted directly into the body. A new synthesis strategy was designed that allows fabrication of all inorganic LEDs via a wet-chemistry approach. Finally, they emit in the ultraviolet region due to careful design of the nanocrystals embedded in the glass.

In traditional LEDs, light emission occurs at the sharp interface between two semiconductors. The oxide-in-oxide design used here is different, allowing 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 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, it is possible to control the electrical response of the whole material.

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