Laser Color Revolution Through Single Nanomaterial Brought About By Engineers

As of now, the laser colors used in a variety of products like BluRay DVD Players or Digital Displays had to be created from different semiconductor materials. There was nothing common in the shape and form of these materials. Addressing this problem, Engineers from Brown University and QD Vision Inc. started working towards building a single nanomaterial that could create many different laser colors. And they have found a breakthrough. These Engineers have become successful in building the first nanoscale single crystals called 'colloidal quantum dots' that can produce the red, green, or blue laser light, a common in digital displays. They achieved this by varying the size of the nanocrystals, making these lasers the first of their kind.

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Vertical-cavity surface-emitting laser Colloidal quantum dots — nanocrystals — can produce lasers of many colors. Cuong Dang manipulates a green beam that pumps the nanocrystals with energy, in this case producing red laser light. Credit: Mike Cohea/Brown University

The colloidal quantum dots are made up of cadmium and selenium alloy and a coating of zinc, cadmium, and sulfur alloy and a proprietary organic molecular glue. During the production phase, a wet chemistry process is used to vary the size of the nanocrystals with precision. For example, 4.2 nanometer cores produce red light, 3.2 nanometer ones emit green light and 2.5 nanometer ones shine blue. This technology is better than the earlier attempts for the same because it needs 10 times less pulsed energy or 1,000 times less power to produce laser light.

As you can see from the image above, Cuong Dang, a senior research associate and nanophotonics laboratory manager in Nurmikko’s group at Brown, while experimenting with brewing a batch of colloidal quantum dots for Brown-designed specifications, found a viscous liquid that Nurmikko said somewhat resembles nail polish. Taking it a step forward, when Dang coated different shapes of glass with this new found liquid, he discovered something amazing. When the liquid evaporated, several densely packed solid, highly ordered layers of the nanocrystals were left on the surface. And upon sandwiching that glass between two specially prepared mirrors, Dang created one of the most challenging laser structures called a vertical-cavity surface-emitting laser or VCSEL. The Brown-led team was the first to make a working VCSEL with colloidal quantum dots.

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