Engineers produce multiple colors of lasers using a single material

Cuong Dang manipulates a green beam that pumps Brown University's new nanocrystals with energy

Ordinarily, if you wanted to include blue, green and red laser light sources in the same device (such as a BluRay player), you would need to build in three separate lasers – each one incorporating different semiconductor materials. Now, however, engineers from Rhode Island’s Brown University have succeeded in creating different colors of lasers, all using the same nanocrystal-based semiconductor. Among other things, this opens the door to digital displays that could produce various colors of laser light simultaneously.

Working with engineers from tech company QD Vision, the Brown team created “nanometer-sized semiconductor particles called colloidal quantum dots or nanocrystals with an inner core of cadmium and selenium alloy and a coating of zinc, cadmium, and sulfur alloy and a proprietary organic molecular glue.”

The size of the nanocrystals/quantum dots, which can be precisely controlled in the production process, is what determines the color of laser beams produced using them – red light comes from crystals with cores measuring 4.2 nanometers across, green light comes from 3.2-nanometer models, while 2.5-nanometer cores result in blue light. Other colors can also be achieved, using core sizes between those points in the spectrum.

While the size of the core is what dictates the color of the light, the crystals’ structure and outer coating also play an important role – they reduce the amount of crosstalk (a form of interference) that occurs in the lasing process, making the technology much more energy-efficient than it otherwise would be. Other researchers have attempted to overcome crosstalk problems simply by boosting the power input, although much of that power ends up being lost as heat.

In order to create lasers using the new nanocrystals, a nail polish-like solution containing the crystals is painted onto a piece of glass. Once the liquid carrier in that solution has evaporated, the glass is then sandwiched between two special mirrors, ultimately resulting in what is known as a vertical-cavity surface-emitting laser. The glass can be cut into a number of shapes, increasing the possible applications of the technology.

“We have managed to show that it’s possible to create not only light, but laser light,” said Arto Nurmikko, professor of engineering and leader of the project. “In principle, we now have some benefits: using the same chemistry for all colors, producing lasers in a very inexpensive way, relatively speaking, and the ability to apply them to all kinds of surfaces regardless of shape. That makes possible all kinds of device configurations for the future.”

A paper on the research was recently published in the journal Nature Nanotechnology.

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