Colloidal semiconductor quantum shells (QSs) represent a breakthrough in nanocrystal lasing technology, addressing the persistent challenge of Auger recombination in conventional quantum dots. The unique CdS/CdSe/CdS spherical quantum well structure of QSs enables exceptional suppression of nonradiative decay pathways, leading to ultralong multiexciton lifetimes and broad optical gain bandwidth. This potential has been demonstrated through integration with nanopillar photonic crystal cavities, achieving record-low lasing thresholds (~4 μJ/cm²) and wide spectral tunability (565-634 nm). The high-quality (Q~6000) nanocavities facilitated precise control over emission wavelengths while maintaining excellent mode confinement, highlighting QSs as a versatile platform for solution-processable lasers. (ACS Nano 2024, 18, 16, 10946–10953)
Lasing emission lines measured at T = 77 K for various array periods Λ. (red) Λ = 365 nm, (yellow) Λ = 335 nm, and (green) Λ = 315 nm.
The exceptional performance of QSs stems from their innovative “inverted” architecture. Their CdS-CdSe-CdS core-shell-shell design induces strong exciton-exciton repulsion, yielding biexciton lifetimes exceeding 10 ns and quantum yields approaching 80%. This geometry creates two distinct gain mechanisms: a long-lived (>6 ns) single-exciton mode immune to Auger decay and a biexciton mode enabling broad amplification bandwidth (~300 meV). Such properties surpass conventional quantum dots and even quasi-2D nanoplatelets, positioning QSs as the premier colloidal gain medium. Quantum confinement engineering in QSs can overcome fundamental limitations in nanocrystal lasing. (ACS Nano 2022, 16, 2, 3017–3026)
(a) Absorption and emission spectra of 4.5 nm-core CdSbulk−CdSe−CdS quantum shells (R CdS = 2.25 nm, H Se = 2 nm and HS =3.75 nm). (b) The photoluminescence intensity decay of 4.5 nm-core CdSbulk−CdSe−CdS quantum shells measured under two excitationregimes with the average number of absorbed photons per QD being equal to ≈ 0.05 (gray curve) and ≈ 1.2 (red curve). The high-power excitation regime reveals an ensemble-averaged biexciton lifetime of τXX = 5.1 ns. The low-power excitation measurement (blackcurve) shows a single-exponential decay with an exciton lifetime of τX = 36 ns (R-value = 0.998). (c) Lagtime-dependence of the cross-correlation function, g2, showing the ratio of biexciton to exciton QY (BX/X QY) for 4.5 nm core (orange curve) and 6.0 nm core (bluecurve) quantum shells.
QS advancements herald a new era for colloidal nanomaterial lasers, combining the benefits of solution processability with performance metrics rivaling epitaxial devices. The demonstrated low thresholds, spectral versatility, and exceptional gain lifetimes make QSs ideal for integrated photonic circuits, quantum light sources, and compact sensor applications. Future development of electrically pumped QS lasers could enable widespread adoption in consumer electronics and biomedical devices, fulfilling the long-standing promise of colloidal nanomaterials in practical optoelectronics.