Quantum-Dots Excited-State Lasing for High-Loss Devices

Electrically pumped lasing in colloidal quantum dots (QDs) is a promising approach for developing solution-processable on-chip light sources. A key step toward this goal is achieving lasing within the high-optical-loss architecture of quantum-dot light-emitting diodes (QLEDs). This necessitates simultaneously high material gain and low population-inversion thresholds, which are challenging to attain with conventional QDs due to constraints like Kasha’s rule and Auger recombination. In this study, a mild photochemical n-doping strategy is applied to cube-shaped CdSe/CdS core/shell QDs to modulate their excited-state transitions. This approach results in a lasing threshold below 3 excitons per QD, a material gain coefficient exceeding 900 cm–1, and a suppression of nonradiative Auger decay, evidenced by an extended biexciton lifetime of approximately 7 ns. These properties facilitate optically pumped, pure excited-state amplified spontaneous emission at room temperature in a functional QLED structure. The findings suggest that engineering excited-state transitions in heavily n-doped gain media can help overcome the limitations of band-edge-dominated gain, providing a potential pathway for realizing electrically pumped QD lasers.