Low-Threshold Lasing in Colloidal InP/ZnSe/ZnS Quantum Dots via ZnSe Interlayer Engineering

Colloidal InP-based quantum dots (QDs) are promising heavy-metal-free emitters for display applications, but their potential for light amplification remains underexplored. Here, we demonstrate lasing in red-emitting InP/ZnSe/ZnS core/multishell QDs with high quantum yield. Increasing the ZnSe interlayer thickness initially lowers the amplified spontaneous emission threshold, but beyond a critical thickness, the threshold rises, although the Auger lifetime increases. Time-resolved spectroscopy reveals that this trend arises from defect states, which capture hot carriers and increase Auger-related losses, demanding higher exciton densities to achieve population inversion. Using InP QDs with tailored ZnSe shell thickness, we construct a liquid-state vertical-cavity surface-emitting laser, which exhibits lasing thresholds of 334 μJ/cm² and 4.3 mJ/cm² under femtosecond and nanosecond excitation, respectively. These results highlight the potential of InP-based QDs as efficient optical gain media and indicate that avoiding defects that capture hot carriers in InP-based QDs is essential for advancing their application in lasers.