Researchers have demonstrated steady state lasing with solution-processed nanoparticles called colloidal quantum dots, an important step on the path to improving laser tools for more accurate medical testing technology and other applications.

The new studies prove the feasibility of steady state lasing with colloidal quantum dots and provide practical guidelines to make them even better as optical-gain media. Improving quantum dot lasing could produce better tools for detailed, cellular-level biochemical analysis.

The team mixed together liquid solutions that contain various quantum dot precursors. When the solutions react, they produce solid quantum dots that stay suspended in the liquid — colloidal quantum dots. Solution-based processing greatly reduces the cost.

Most quantum dot lasers are limited to pulses of light lasting just a few nanoseconds. The team overcame this problem by changing the shape of the quantum dots, rather than their size. They created quantum dots with a spherical core and a shell shaped like a flying saucer.

The mismatch between the shape of the core and the shell introduces a tension that spreads apart the electronic states of the quantum dot, lowering the amount of energy needed to trigger the laser. Unusually narrow emission linewidths increase the relative fraction of the dots participating in light amplification and helps further reduce the lasing threshold.