Colloidal quantum dots enable tunable liquid-state lasers

Present-day liquid-state lasers are based on organic dyes. Here we demonstrate an alternative class of liquid lasers that use solutions of colloidal quantum dots (QDs). Previous efforts to realize such devices have been hampered by the fast non-radiative Auger recombination of multicarrier states required for optical gain. Here we overcome this challenge by using type-(I + II) QDs, which feature a trion-like optical gain state with strongly suppressed Auger recombination. When combined with a Littrow optical cavity, static (non-circulated) solutions of these QDs exhibit stable lasing tunable from 634 nm to 575 nm. These results indicate the feasibility of technologically viable dye-like QD lasers that exhibit broad spectral tunability and, importantly, provide stable operation without the need for a circulation system—a standard attribute of traditional dye lasers. The latter opens the door to less complex and more compact devices that can be readily integrated with various optical and electro-optical systems. An additional advantage of these lasers is the wide range of potentially available wavelengths that can be selected by controlling the composition, size and structure of the QDs.