A New Generation of Liquid Lasers from Engineered Semiconductor Nanocrystals with Giant Optical Gain

Abstract With the development of optofluidic technology, liquid lasers have attracted intense interest but still face a formidable challenge due to the lack of qualified gain media and creative device design. Compared to the organic fluorescent dyes and traditional CdSe‐based nanocrystals (NCs), the lead‐halide perovskite (LHP) NCs feature larger gain coefficient and higher robustness, which renders LHP NCs a promising unexploited liquid gain medium. Herein, for the first time, the hidden principle governing the solution‐based light amplification in LHP semiconductor NCs is demystified and it is demonstrated that the LHP NCs are superior solution‐phase gain media showing a giant (≈2600 cm −1 ) optical gain. On this basis, a novel microfluidic laser device is designed and realized that exhibits a record‐low pump threshold (≈22.7 µJ cm −2 ), high Q‐factor (≈7480), large output polarization (≈0.91), and long‐time robustness over high‐intensity operation, which is readily applicable to practical applications. The findings represent a significant step toward the technologically important liquid lasers of the new generation and can advance optofluidic applications.