Multiexcitonic Lasing in Thin-Shell Colloidal Quantum Dot Supraparticles

High Resolution Image Download MS PowerPoint Slide Self-assembled supraparticles (SPs) of colloidal semiconductor nanocrystals act as solution-processable microlasers, where optical gain couples to whispering-gallery modes supported by the microspherical cavity. Here, multicolor lasing is demonstrated from SPs composed of standard-size (5.5–6.5 nm), graded thin-shell CdS x Se 1– x /ZnS quantum dots (QDs) by exploiting their electronic transitions. While lasing from higher-order states typically requires engineered thick-shell QDs, we achieve this using conventional thin-shell QDs through composite SPs that integrate two QD populations: one with an absorption edge above the pump wavelength (625 nm) and another with an edge near (540 nm) or below (450 nm) the pump (532 nm). At low pump fluence, lasing occurs in the red region (2.00–2.04 eV) from 1S transitions. With increased fluence, lasing shifts to the yellow region (2.14–2.18 eV), arising from 1P transitions. This fluence-controlled red-to-yellow shift establishes composite SPs as a versatile platform for tunable, multicolor microlasers based on standard-sized QDs.