Wu Kaifeng, a researcher at the Chinese Academy of Sciences Dalian Institute of Chemical Physics, and Yang Yang, an associate researcher, have prepared a low toxic blue light colloidal quantum dot with excellent optical performance, and used its solution as the optical gain medium to achieve a highly stable liquid laser output. This study is of great significance for promoting the practical application of colloidal quantum dots in the field of lasers. The relevant research results were recently published in Nature Nanotechnology. Colloidal quantum dots have the advantages of tunable spectra, high luminescence purity, and low cost, and have attracted widespread attention in the field of lasers. The research team has prepared high-quality blue light ZnSe/ZnS core-shell quantum dots. The quantum dot is compact in size and has a spontaneously formed gradient shell component. Its "smooth" confined potential well helps to suppress non radiative Auger recombination, thereby extending the lifetime and gain lifetime of excitons. Subsequently, the team used femtosecond transient absorption spectroscopy to study the multi exciton recombination dynamics and optical gain behavior of the quantum dot, and found that it has a double exciton optical gain lifetime of nearly 1 nanosecond. This lifetime is nearly an order of magnitude higher than that of ZnSe core quantum dots of the same volume, approaching the previously reported optical gain lifetime of complex core-shell quantum dots with a diameter of 20 nanometers. The advantages of compact size and long gain lifetime make this quantum dot promising as a "dye" in solution, achieving liquid laser output. The team further utilized femtosecond and nanosecond lasers to pump quantum dot solutions, achieving low threshold blue light amplification spontaneous emission with high gain coefficients. Under nanosecond quasi continuous optical pumping, the quantum dot solution successfully achieved laser output in a classical Littrow laser cavity. The output laser has the characteristics of low threshold, good directionality, narrow linewidth, continuous adjustment, good coherence, and high polarization degree. This quantum dot liquid laser can achieve long-term stable output without stirring or cycling, which is more than two orders of magnitude more stable than blue dye molecules in the same wavelength band. This work fully demonstrates the practical application potential of colloidal quantum dots in liquid lasers, and also provides new opportunities for the application of quantum dots in fields such as optohydrodynamics, biological imaging, and diagnostics. (New Society)