Red, Green and Blue Liquid‐Film Lasers Based on Colloidal Quantum‐Dots

Colloidal quantum dots (cQD) are heralded for their tunable bandgaps, solution-processibility, and cost-effectiveness, making them ideal candidates for lasing applications. However, previous cQD lasing demonstrations have largely depended on close-packed solid-state films, which are deemed essential to counteract the rapid decay of material gain. In this study, a novel approach is introduced utilizing "entropic ligands and solvent" to enhance the solubility of cQDs in solution. By achieving the necessary critical volume fraction for lasing, this strategy leads to the groundbreaking development of the first liquid-state vertical-cavity surface-emitting lasers (VCSELs) based on cQDs across the blue and green spectrum, encompassing diverse material systems such as CdSe-based and InP-based cQDs. Furthermore, by integrating the liquid-state VCSEL with a microfluidic channel, it is demonstrated that heat dissipation during intense excitation is pivotal for cQD lasing likely across various excitation modes-whether pulsed or continuous-wave, optically or electrically-pumped-and different media, including liquid and solid states. The research will lay the foundation for a new era of liquid-state cQD lasers for specific occasions, distinguished by their customizable and largely-variable wavelengths, compact form factors, diverse materials basis, and dependable performance.