Deep-Red to Near-Infrared Vertical Cavity Surface-Emitting Lasers from Bipyramidal Weakly Confined Quantum Dots

Abstract

Colloidal quantum dots (QDs) are attractive solution-processable gain media for next-generation laser devices. To date, the canonical metal-chalcogenide QDs have demonstrated superior optical gain across blue, green, and red spectral ranges. However, it is still challenging to access the technologically important deep-red to near-infrared region due to the bandgap limitation of existing QDs. Here, we address the gap by demonstrating low-threshold deep-red to near-infrared optical gain from weakly confined CdSe/CdS QDs. By developing a synthetic strategy toward high-quality bipyramidal CdSe cores and controlled shell coating, we tune the stimulated emission from 660 to 720 nm, a wavelength beyond the intrinsic bandgap limit of bulk CdSe. The mechanistic investigation by transient spectroscopy reveals that the gain origin shifts from biexciton recombination in naked CdSe QDs to electron–hole plasma (EHP) emission in core–shell QDs owing to carrier wave function leakage into the shell. Such weak confinement design demonstrates substantial suppression of Auger recombination in the EHP regime, indicating the potential for high-power devices. Building on these findings, we fabricate a vertical cavity surface-emitting laser that achieves low-threshold deep-red to near-infrared lasing over 690–725 nm.