German and Spanish scientists have used luminescent proteins to create a pure white organic LED, at a lower cost than today’s conventional devices.
The ‘BioLED’ uses proteins packaged in the form of rubber. Red, green and blue rubber layers cover a single LED, producing white light. Today’s white LEDs produce light that lacks a red component, and so are colder (and potentially harmful, as blue light suppresses melatonin production) than incandescent lights.
To form the device, luminescent proteins were introduced into a polymer matrix, producing luminescent rubber. These are only stable in an aqueous buffer solution, and so standard coating procedures were not suitable. Thus, a new coating technique had to be developed.
A gel was used to embed the proteins, consisting of a concentrated aqueous protein solution and a polymer compound. The polymers binds the solution to make a gel-like network, while ensuring that the necessary moisture is retained. The gel was then vacuum-dried, turning it into a rubber-like material suitable for multilayer coating of LEDs, which also protects the proteins.
The rubbers are excited by a conventional blue or ultraviolet LED, which is cheaper to produce than a white unit. White LEDs use the expensive material YAG:Ce (cerium-doped yttrium aluminum garnet), which is replaced by proteins in the new devices.
A blue LED is combined with green and red rubber layers, or ultraviolet with red, green and blue layers. The result is white light containing equal parts red, green and blue, while maintaining the efficiency of inorganic LEDs.
The proteins are low-cost and biodegradable, said study co-author Rubén D. Costa. They also have “luminescent properties that remain intact during the months of storage under different environmental conditions of light, temperature and humidity.”
Work is now ongoing to achieve greater thermal stability and a longer operating lifetime. The chemical composition of the polymer matrix is also being optimised, in addition to using proteins that are more resistant to device operating conditions.
The research was published in Advanced Materials; see http://tinyurl.com/hbxylqy.
This work was published in August last year, but only recently came to our attention. (TA)