Quantum-dot light emiting diodes can outshine their rivals: Study

December 11th, 2007 - 2:58 pm ICT by admin  

Washington, Dec.11 (ANI): The size of the quantum dots can be tuned to produce several different colours, and a study has opined that quantum-dot light-emitting diodes (LEDs) require just three to four volts of electricity to run non-stop for over 300 hours.
The study further suggests that the brightest quantum-dot LEDs can provide lighting for displays that are clearer and richer in colour, as well as being cheaper to make, than existing ones.
The devices could be used to make better displays for mobile phones and Personal Digital Assistant (PDAs), and to light larger flat-panel TV screens, claim Chinese and American researchers.
Quantum dots are nanoscale semiconductors that confine electrons in three dimensions. In this case, the quantum dots have a cadmium selenide core and a zinc sulphide “shell”.
Electrons are excited to higher energy levels in the core and the shell, then fall into the empty spaces, or “holes”, left behind. The dot then forms an “exciton” and emits a particle of light.
Changing the size of a QDLED makes it emit a different wavelength of light producing red, orange, yellow, or green light.
Although standard LEDs are far more efficient, QDLEDs could be better in other ways.
The range of colours and intensity of light produced by QDLEDs promise to be better than alternative technologies.
“The brightness of the best LCD monitor on the market today is 500 candelas per square metre and the brightness of room light is about 2000 cd/m2,” says Andrew Wang of Ocean NanoTech in Fayetteville, Arkansas, which developed the quantum dots.
“Our QDLEDs have reached 9000 cd/m2 in brightness, which makes them the brightest in the world.”
QDLEDs are also relatively easy to make, using solution-processing techniques, such as spin coating, ink-jet printing and roll-to-roll printing, which is useful for flexible-screen applications.
The Ocean NanoTech researchers, together with Yongfang Li and Qingjiang Sun at the Chinese Academy of Sciences, are now working hard to optimise the structures of the quantum dots to further increase the lifetime and power efficiency of the devices.
For the technology to be incorporated into a product, however, it may be necessary to demonstrate the same physical phenomena using a material other than cadmium, which is a highly toxic heavy metal. (ANI)

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