Colloidal-Quantum-Dot Ring Lasers with Active Color Control

Boris Le Feber, Ferry Prins, Eva De Leo, Freddy T. Rabouw, David J. Norris*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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.

Original languageEnglish
Pages (from-to)1028-1034
Number of pages7
JournalNano Letters
Volume18
Issue number2
DOIs
Publication statusPublished - 14 Feb 2018

Keywords

  • colloidal quantum dots
  • core/shell nanocrystals
  • giant-shell nanocrystals
  • Quantum-dot lasers
  • template stripping
  • ultrafast switching

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