Biphasic interface-regulated ultrastable narrow-linewidth colloidal quantum well liquid lasers

Liquid nanocrystal microlasers are promising miniaturized coherent light sources, yet their development remains constrained by the difficulty of simultaneously preserving colloidal gain media, stabilizing liquid-cavity morphology, and maintaining low-loss optical feedback. Here, we report, to the best of our knowledge, the first colloidal quantum well (CQW)-based biphasic liquid microsphere laser and establish biphasic interfacial engineering as an active strategy for liquid nanocrystal lasing. Green-emitting CdSe/CdSe_1-xS_x core/crown CQWs and red-emitting CdSe/Cd_1-xZn_xS core/shell CQWs are incorporated into glycerol/toluene biphasic microspheres to construct whispering gallery mode (WGM) microlasers with chromaticity-tunable emission. The glycerol/toluene interface functions as a multifunctional regulatory boundary that stabilizes the spherical microcavity, preserves the CQW microenvironment, and provides refractive-index contrast for WGM confinement. Consequently, the green- and red-emitting CQW microsphere lasers show low-threshold, spectrally pure lasing with a linewidth of ~0.02 nm, a polarization degree of 0.923, and a quality factor up to 3.27 × 10⁴. The red-emitting device exhibits negligible decay after 800 min at 10-fold threshold pumping. Furthermore, co-confinement of red and green CQWs within a single microsphere enables continuously tunable dual-color lasing. These results establish biphasic liquid-liquid interfaces as active mediators of nanocrystal photophysics, cavity stability, and optical feedback for stable and chromaticity-tunable liquid microlasers.