nanotechnology
The development of high brightness white LEDs has opened up several important new markets for LEDs. Their use as backlights for LCD displays has emerged as the first main market. This is currently a multi billion dollar industry and is set to grow as white LEDs are used in ever-larger displays. Further into the future, white LEDs are beginning to have a substantial impact on the general lighting industry and their use in this area is entering a period of rapid growth driven by the substantial energy savings offered by these devices.
At present, the majority of white LEDs chips on the market consist of a blue LED combined with a yellow phosphor and luminous efficiencies are in excess of 100 lm/W. However the white light produced using this approach is bluish and lacks warmth. In order to improve the colour, red green and blue light can be combined, therefore new red and green phosphors need to be developed. With current technology it is difficult to produce new phosphors that span the whole gamut of colours and can be excited by blue light.
nanophosphor research at sharp laboratories of europe
At SLE we are investigating a new class of phosphors called colloidal quantum dots (QDs). These are small semiconductor nanocrystals (2-10 nm diameter) prepared by a wet chemical synthesis. The unique property of these phosphors is that the colour of light they emit can be tuned by simply altering the size of the nanocrystals.
Fluorescence image of colloidal QDs of
different size
Some commercially available QDs contain undesirable materials such as cadmium, so at SLE we are developing synthetic strategies to prepare materials based on non-toxic III-V semiconductors. This work is carried out in SLE’s fully equipped chemistry facility. QDs prepared in this way are coated with a shell of organic capping groups allowing solubility in a range of organic solvents and polymer resins for integration with LEDs.
nanowire research at sharp laboratories of europe
In the future, for SSL to be adopted globally there will be a need for it to be much cheaper and more flexible. One route to potentially achieve these features is to make LEDs chips with much smaller dimensions, but with higher efficiency. In principle, large flexible substrates or glass sheets could be printed or patterned with LEDs with dimensions of a few hundred nanometres to produce flexible lighting or displays.
At SLE we are investigating a new type of LED made from nanowires of III-nitride semiconductors grown, within our laboratories, by a range of techniques such as chemical vapour deposition (CVD) and molecular beam epitaxy (MBE).
SEM picture and schematic diagram of a semiconductor nanowire LED
The light emitting properties, such as emission wavelength and efficiency, of the nanowires can be tailored by changing their dimensions and by adding multiple layers of different semiconductor composition and electrical conductivity around the nanowire core. We use our fully equipped cleanroom to fabricate the grown nanowires into actual tiny LED devices.
