Green Light from Red-Emitting Nanocrystals: Broadband, Low-Threshold Lasing from Colloidal Quantum Shells in Optical...

Spherical semiconductor nanoplatelets, known as quantum shells (QSs), have captured significant interest for their strong suppression of Auger recombination, which leads to long multiexciton lifetimes and wide optical gain bandwidth. Yet, the realization of benefits associated with the multiexciton lasing regime using a suitably designed photonic cavity remains elusive. Here, we demonstrate broadly tunable lasing from close-packed films of CdS/CdSe/CdS QSs deposited over nanopillar arrays on Si substrates. Wide spectral tuning of the stimulated emission in QSs with a fixed bandgap value was achieved by engaging single exciton (λ ∼ 634 nm), biexciton (λ ∼ 627 nm), and multiple exciton (λ ∼ 615-565 nm) transitions. The ensemble-averaged gain threshold of <N> ∼ 2.6 electron-hole pairs per QS particle and the low photonic cavity fluence threshold of ∼4 μJ/cm² were attributed to Auger suppression. The tuning of the lasing emission closely aligns with our model predictions achieved by varying the array period while preserving mode confinement and quality (Q) factors. These results mark a notable step toward the development of colloidal nanocrystal lasers.