Making tiny, tunable lasers from nano wires is now possible thanks to scientists at Berkeley Lab, the devices could have applications in optoelectronics and elsewhere.

Peidong Yang explains that the simple chemistry precludes many of the problems of standard nanowire production, such as expensive equipment and high temperatures. The approach adopted by the Berkeley team is a chemical-dipping solution process that allows them to make a self-assembled blend of nanoscale crystals, plates and wires composed of cesium, lead and bromine (CsPbBr3); the same material successfully used in experimental high-efficiency photovoltaics. [Yang et al., Proc Natl Acad Sci (2016) 113, 1993-1998; DOI: 10.1073/pnas.1600789113]

"The whole purpose of developing nano-sized lasers is to interface photonic (light-based) devices with electronic devices seamlessly at scales relevant to today's computer chips," explains Yang. "Today, these photonic devices can be bulky."

Yang's team actually pioneered nanowire lasers almost 15 years ago using zinc oxide (ZnO) and gallium nitride (GaN), but these had limited tunability, low brightness and were expensive. Now, they have demonstrated how dipping a thin lead-containing film into a methanol solution containing cesium, bromine and chlorine heated to about 50 degrees Celsius produces crystalline structures formed, including nanowires between 2 and 40 micrometers in length and with diameters from 200 nanometers to 2.3 micrometers.

The team plucked the most promising nanowires from their crystal garden and placed one on a quartz base and excited it with a laser source to induce emission. An ultrafast visible or ultraviolet laser pulse stimulated a 1 GHz pulse from the nanowire laser, which Yang says demonstrated remarkable stability although they are sensitive to moisture. These nanowire lasers may be the first of a new class of inorganic perovskite-type device and Yang suggests they might be tuned from visible green to blue wavelengths.

It might be possible to protect these nanowire lasers from moisture by coating them with a polymer layer, the team suggests. Another requirement of future work will perhaps be to see whether tin might be used instead of toxic lead to make the devices safer and easier to recycle at end of life.

This field and the focus on perovskite structures is developing rapidly, Yang asserts. He points out that even though his team jumped into this specific field only twelve months ago, they have already developed tunable lasers that are amazingly bright emitters. "It's just so exciting," he says.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".