LINKOPING UNIVERSITY -Luminous wallpaper closer to reality
(ENP Newswire Via Acquire Media NewsEdge) ENP Newswire - 01 March 2013
Release date- 01032013 - Three new theses from Magnus Willanders' research group provide new knowledge of white zinc oxide LEDs: They can kill cancer cells, and be grown on large surfaces for wallpaper or curtains.
The colour can be changed with the addition of a layer of polymers, and they shine more brightly if they are hollowed out.
The change from incandescent or low-energy bulbs to LEDs is well under way; both IKEA and others in the industry are now selling fixtures with different types of white LEDs. If we were to change out all the incandescent bulbs for LEDs, energy consumption would decrease by 20 % at a stroke. Illumination represents a whole 25 % of Sweden's energy consumption, so there are many good reasons to look closer at white LEDs.
Professor Willander and his research group in the physics and nanotechnology group on Campus Norrkoping are studying a great number of things, including white zinc oxide LEDs.
The advantage of zinc oxide nanostructures is that they can be grown easily and cheaply on almost any material at all - paper, plastics, or semiconductors. Zinc oxide is catalytic, piezoelectric (mechanical energy converts into electricity) and is also biocompatible. This means that there is a large range of uses for different types of zinc oxide nanostructures.
'We can manufacture white LEDs in large sheets that can be used as luminous wallpaper or curtains, or for lamps without wall outlets, but they can also be used for photochemical processes in the body - in a cell or in the mouth. Zinc oxide nanostructures can also be used as sensors that measure various substances in the cell and send the measurement data direct to your mobile phone,' Willander says.
Over the fall and winter, three PhD students defended three theses containing new knowledge about white zinc oxide LEDs. In two of them, zinc oxide was also combined with copper oxide and polymers.
Sadaf Jamil Rana worked with photochemical processes. Owing to defects in the material, zinc oxide nanothreads emit photons in the form of perfect white light, which is why they are so well adapted for LEDs. Rana got these nanothreads to grow on the tip of a thin pipette. With the help of the pipette, this LED can then be introduced into a human cell - a cancer cell, for example. When the photon is emitted, radicals are formed that - simply put - poison the cell so it dies.
Rana has even gotten these LEDs to shine extra brightly.
When nanothreads are grown, they form a thick 'forest', but Rana has also managed to hollow them out so that they more resemble a pipe a few nanometers long.
'It's the thin edge that emits the light, and it's extra strong due to the defects in the material coming through better,' Willander says.
One of the other PhD students, Saima Zaman, instead worked on growing zinc oxide nanostructures in large sheets on paper, which could for example be used for luminous wallpaper.
She has also managed to affect the strength and colour of the light through laying on polymers in different concentrations. Low concentrations yield bluer light, while higher concentrations yield greener light. By mixing several different polymers, she can also produce various optical properties. In one of the seven articles from the thesis, several of which were published in Applied Physics from the publisher Springer, she and her PhD student colleague Ahmed Eltahir Elsharif Zainelabdin describe how the whole thing works.
Together, they have also grown copper oxide nanostructures, which are 'p-type' (having a surplus positive charge) alongside zinc oxide nanothreads, which are a natural 'n-type' semiconductor (having a surplus negative charge). (At right: zinc oxide nanothread has small outgrowths, or 'leaves', of copper oxide)
Zainelabdin then researched what optical properties could be produced with a zinc oxide/copper oxide combination. He found that the light emitted covered the entire visible spectrum plus the ultraviolet range. He also successfully produced electrochemical sensors, including a very sensitive moisture sensor and a pH sensor (which measures acidity).
The same technology can thus be used for many different applications. But what's special about white LEDs that Willander and his group are working on is that they are simple and cheap to manufacture, even on an industrial scale. Nor do they contain and substances that are harmful to the environment. The lamps and fixtures of the future can thus be cheaper, more environmentally friendly, and more imaginative than they are today.
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