Quantum dots (QDs) were recognized by the 2023 Nobel Prize in chemistry. As mentioned by the Nobel committee, in addition to their well-established applications in display, QDs will find many more applications to benefit humankind. One long sought-after application is QD-lasing, which seems to be straightforward given the intense and color-tunable emission of QDs.
Over the years, a number of core/shell heterostructured QDs (primarily CdSe-based core/shells) with impeded Auger recombination have been developed. These efforts have led to several milestones in the development of QD-lasing technologies, such as sub-single-exciton low threshold lasing, continuous-wave lasing, and electrically-driven amplified spontaneous emission. However, due to the large size (10 to 20 nm) of the Auger-suppressed QDs used in these studies, these devices almost exclusively lase in the red part of the spectrum. This limitation leaves technologically-viable blue QD-lasers remaining out of reach, despite blue lasers are crucial to laser-based display, printing, manufacturing, data recording, and medical technologies.
Recently, Prof. WU Kaifeng's group and his coworkers from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences have achieved stable blue lasing from a solution of low-toxicity colloidal QDs. The study was published in Nature Nanotechnology.
The researchers developed very compact (7.8 nm) ZnSe/ZnS core/shell QDs, yet their gain lifetime was approaching one nanosecond, which was comparable to the best CdSe-based complex core/shell systems with diameters typically of about 20 nm. A crucial enabler to this success was the suppression of nonradiative Auger recombination by an unintentionally alloyed core/shell interface that smoothened the confinement potential. Due to the compact size (thus minimized scattering loss) and long gain lifetime, the researchers could handle these QDs just like laser dyes, demonstrating tunable and robust liquid lasing output from a Littrow cavity under excitation by solid-state nanosecond lasers.
"Beyond making a significant advancement in blue QD lasing, the liquid laser based on ZnSe/ZnS QDs offers many practical benefits,” said Prof. WU. “They don't contain toxic elements such as Cd and Pb, and hence are more compatible with real lifetime applications, and they exhibit stability against photodamage that far exceeds typical blue dyes, allowing for consistent output needing circulation systems.”
Therefore, this blue liquid laser not only serves as a promising replacement of blue dye lasers for existing technologies, but it can also fill the "blue gap" of QD lasers using environmentally benign QDs for a multitude of emerging applications.