Colloidal-Quantum-Dot Ring Lasers with Active Color Control

Abstract

To improve the photophysical performance of colloidal quantum dots for laser applications, sophisticated core/shell geometries have been developed. Typically, a wider bandgap semiconductor is added as a shell to enhance the gain from the quantum-dot core. This shell is designed to electronically isolate the core, funnel excitons to it, and reduce nonradiative Auger recombination. However, the shell could also potentially provide a secondary source of gain, leading to further versatility in these materials. Here we develop high-quality quantum-dot ring lasers that not only exhibit lasing from both the core and the shell but also the ability to switch between them. We fabricate ring resonators (with quality factors up to ∼2500) consisting only of CdSe/CdS/ZnS core/shell/shell quantum dots using a simple template-stripping process. We then examine lasing as a function of the optical excitation power and ring radius. In resonators with quality factors >1000, excitons in the CdSe cores lead to red lasing with thresholds at ∼25 μJ/cm2. With increasing power, green lasing from the CdS shell emerges (>100 μJ/cm2) and then the red lasing begins to disappear (>250 μJ/cm2). We present a rate-equation model that can explain this color switching as a competition between exciton localization into the core and stimulated emission from excitons in the shell. Moreover, by lowering the quality factor of the cavity we can engineer the device to exhibit only green lasing. The mechanism demonstrated here provides a potential route toward color-switchable quantum-dot lasers.

Composite Structures with Emissive Quantum Dots for Light Enhancement

“…On the other hand, highly directional lasing requires highly asymmetrical structures, e.g., elliptical microdisks with notches, which cannot be readily printed . Thus, QD based microcavities have been fabricated by using lithography processes such as photolithography and EBL since it can provide higher resolution down to subwavelength scale . Importantly, one can predefine the size and shape of microcavity precisely by creating a resist template of any preprogrammed shape.…”

“…Besides the top‐down approach, template stripping is another high‐resolution lithographic technique that can be used to fabricate QD microcavities . EBL and reactive‐ion etching were used to create trenches of circular rings (≈500 nm deep) on silicon templates ( Figure a) .…”

Over 1000‐Fold Enhancement of the Unidirectional Photoluminescence from a Microsphere‐Cavity‐Array‐Capped QD/PDMS Composite Film for Flexible Lighting and Displays

“…Over the past decades, semiconductor quantum dots (QDs), especially binary II‐VI compounds (e.g., CdSe), have been widely investigated and employed in light‐emitting diodes, lasers, and biomarkers for displays and labeling owing to their transparency, solution processability, broad absorption, high quantum yield (QY), tunable bandgap, and sharp emission spectrum . In recent years, the development of flexible lighting/display devices has required the integration of luminescence materials on flexible substrates with the characteristics of luminescence properties and the capability to be stretched into arbitrary shapes.…”

P‐9.1: QD based color converter with DBR Structure and its application on Micro‐LED

“…In recent years, quantum dots (QDs) have been widely used for full-color display and white lighting due to their narrow bandwidth emission, precisely tunable peak wavelength and high luminance efficiency, [1,2] for example, as enhancement films in backlights for LCDs and as replacement for color filters. [3,4] Moreover, the QDs have also been extensively incorporated in GaN based LED display as color converters, where RGB colors were down-converted by exciting according QDs using ultraviolet (UV) or blue LEDs.…”