Ambient‐Stabilized Cadmium‐Free Pure‐Blue Colloidal Quantum Dot Supraparticle Microlasers for Proof‐of‐Concept Low‐Speckle Projection

ABSTRACT Pure‐blue colloidal quantum dot (CQD) lasers are attractive light sources for projection and other display applications, yet high‐performance devices still rely on cadmium‐based QDs. Cadmium‐free ZnSeTe/ZnS CQDs offer a viable alternative, but developing laser platforms that combine ambient operational stability with low‐speckle imaging remains challenging. Here, we report ambient‐stabilized pure‐blue microlasers based on self‐assembled ZnSeTe/ZnS CQD supraparticles (SPs) conformally encapsulated with an ultrathin Al 2 O 3 shell. The spherical SPs support whispering‐gallery‐mode (WGM)‐dominated lasing with a representative threshold of 33 µJ cm − 2 . Deposited by atomic layer deposition (ALD), the Al 2 O 3 shell suppresses oxygen ingress. As a result, the operational half‐life of the SP microlasers increases by more than two orders of magnitude, while the mean lasing threshold decreases from 36 µJ cm − 2 for the pristine SPs to 26 µJ cm − 2 for the 15 nm Al 2 O 3 ‐coated SPs. The weak mutual coherence among individual SP microlasers further enables strong speckle suppression, yielding a speckle contrast of 0.015, well below the human perception limit. Using this ensemble source, we demonstrate a proof‐of‐concept low‐speckle projection system with blue‐emission chromaticity coordinates close to those of the BT.2020 blue primary.