High-Quality Microfluidic Lasers from Water-Soluble Semiconductor Quantum Dots with Auspicious Optical Gain

Abstract

Water-soluble quantum-dot (w-QD) lasing is crucial for the emerging fields of optofluidics, biophotonics, and diagnostics. However, the existing w-QDs are not competent due to their inferior optical gain and poor photostability. Herein, a hydrophilic ligand screening criterion is established to find suitable candidates for developing w-QD lasers. The comprehensive spectroscopic characterizations reveal that the thioglycolic acid-capped w-QDs exhibit superior gain performance that is on par with those of state-of-the-art nonpolar QDs, including the long gain lifetime, large gain cross-section, and low threshold of amplified spontaneous emission. The mechanistic study based on transient absorption and first-principles calculation discloses that the auspicious gain is enabled by the large surface binding energy, small absolute redox potential, and exceptional dispersibility of the w-QDs. On this basis, a novel high-quality microfluidic laser is constructed from the w-QDs, exhibiting a low threshold, high Q-factor, and long-term robustness. The findings represent a significant step toward w-QD lasers and may unlock new possibilities for advanced optofluidics and medical imaging.