Now, pure white light can be produced using zinc, which is usually used to protect iron from rusting and in making brass.
The most commonly used method of producing white light is by mixing three primary colour–emitting phosphors in a proportionate composition. The existing methods of white-light production are energy-intensive and involve a long process.
But the new LED device requires only a single active layer of zinc-based metal–organic framework to get perfect white light under UV-excitation. And synthesis of the zinc framework is easy and highly stable and is not energy-intensive.
Scientists from Indian Association for the Cultivation of Science (IACS), Kolkata, synthesised the zinc-framework and the results were published in Journal of Materials Chemistry C.
“Zeolite, a rare earth mineral, is also used for producing white light. But this is not environment-friendly. Our LED device uses zinc, one of the most abundant metals on earth, to do the work,” explains Shyamal K Saha, Department of Materials Science at the Institute and corresponding author of the paper.
For the LED fabrication, indium tin oxide–coated glass was used as anode and vacuum evaporated aluminium as cathode. “The zinc-based framework is used as the active layer in which electrons are recombined to produce white light. The precursor materials used to make the LED are easily available and very much cost effective,” he adds. By checking with the International Commission on Illumination (CIE) standards, the researchers found that the emission was very close to that of ideal white light.
“The molecules were found to be very stable, and the whole crystalline network was stable up to 500 degree Celsius” says Saptasree Bose, Research Associate and co-author of the paper.
While commercially available white LEDs show slightly higher blue emission when compared with two other primary colours, the new white LED emits three primary colours proportionally to get perfect white light.
“We calculated the energy levels and the origin of photoluminescence. Emissions were obtained at three different wavelengths (384nm, 468nm, 570nm) under UV-excitation,” says Tuhina Mondal, PhD scholar at the institute and first author of the paper. “The final LED requires 8V, which is a bit higher than commercially available LEDs. We are working to minimise this.”