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.
Disentangling carrier kinetics is of both fundamental and technological importance for optoelectronics, while the hole-state dynamics in Cd chalcogenide quantum dots (QDs) remains far from understood. Herein, we take the CdZnS-based alloyed QDs as the model system to examine the hole-state dynamics by transient absorption (TA) spectroscopy. The spectroscopic signature of the hole states could be directly manifested from the TA spectra, even in low-quality CdZnS QDs, which arises from the distinctive features of alloyed QDs. By completely passivating the hole traps, the resulting CdZnS/ZnS QDs feature a significant hole contribution of 17% to the TA bleach and associated bleach buildup kinetics. These merits endow the CdZnS-based QDs with excellent optical gain properties, where an ultralong gain lifetime (1.1 ns) and a broad gain bandwidth (>300 meV) have been observed thanks to the positive trion-suppressed Auger recombination and the retarded hot hole cooling under high excitation intensities. Such a slow hot carrier cooling (200 ps) in the alloyed QDs further indicates their potential in other optoelectronic devices, such as the hot carrier solar concentrators. These findings clarify the characters of the valence band hole and offer insights into the manipulation of hole states for optimizing device performances.
Optical gain in solution-processable quantum dots (QDs) has attracted intense interest toward next-generation optoelectronics; however, the development of optical gain in heavy-metal-free QDs remains challenging. Herein, we reveal that the ZnSe 1−x Te x -based QDs show excellent optical gain covering the violet to near-red regime. A new gain mechanism is established in the alloy QDs, which promotes a theoretically threshold-less optical gain thanks to the ultrafast carrier localization and suppression of ground-state absorption by the Te-derived isoelectronic state. Further, we disclose that the hot-carrier trapping represents the main culprit to exacerbate the gain performance. With the increase of Te-to-Se ratio, a sub-band-gap photoinduced absorption (PA) appears and extinguishes the optical gain. To overcome this issue, we modulate the inner ZnSe shell thickness, and the gain is recovered by reducing the overlap between the gain and PA regions in the Te-rich QDs. Our finding represents a significant step toward sustainable QD-based optoelectronics.
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