In what is being as touted as a major breakthrough, researchers at the Indian Institute of Science (IISc), Bangalore, have discovered a method that can make bulbs and LED-based systems, including TVs and computer screens, cheaper while also improving their brightness.
The findings, which will also reduce electricity consumption, can be used to send photons or light particles into human bodies. This will have applications in the medical sphere, notably in the detection of cancer cells as photons would make them glow with a distinctive colour.
The discovery is related to the light-emitting characteristics of manganese, a metal used in the manufacture of bulbs and displays. Currently, tiny particles, called quantum dots, are being used in electronic displays and lights.
These are mixed with a tiny amount of metals like cadmium and manganese to make them stable. However, cadmium is highly toxic and harms the body. On the other hand, if manganese is used in these quantum dots, they would only glow in orange colour, unlike bulbs using cadmium, which emitted multiple colours.
Dipankar Das Sarma, Professor and Chairman of the Solid State and Structural Chemistry unit at IISc, and his student Abhijeet Hazarika took a very diluted solution of these nanoparticles, that used manganese, under a microscope.
They found that each of them glowed with a different colour. Sarma said, “The traditional emission spectra of manganese was wide because of colours from a wide array of particles. However, all we saw was orange. We could see the real colours only when the particles were diluted.”
Manganese is added in very small quantities to make quantum dots stable and prevent self-absorption. Scientists have learnt that the ‘band gap’ of this structure, however, cannot be changed, leading to a single colour, orange. Band gap is the space in the structure of insulators, a category of materials, where electrons move about. These band gaps can be changed and colours emitted by electrons will vary accordingly. However, such structures are not stable and one photon may absorb another, leading to zero emission of coloured light.
What scientists at IISc observed was that different quantum dots with manganese had different colours. “A quantum dot’s colour depends on whether most of its manganese is near the surface or near the centre of the nanoparticle,” explained a member of the team.
With this technology, researchers can use manganese-doped samples that would have all colours in the spectrum, unlike only orange, while retaining its long-term stability and absence of self-absorption.