Single-mode lasing from colloidal water-soluble CdSe/CdS quantum dot-in-rods

TL;DR

This paper demonstrates water-soluble CdSe/CdS quantum dot-in-rods with maintained luminescent properties, enabling single-mode lasing in micro lasers with low thresholds, through ligand exchange and optimized nanostructure design.

Contribution

It introduces a ligand exchange method to make CdSe/CdS quantum dot-in-rods water-soluble while preserving their optical properties, facilitating low-threshold single-mode lasing.

Findings

Water-soluble quantum dot-in-rods exhibit amplified spontaneous emission.

Micro lasers fabricated from these dots show single-mode operation.

Lasing thresholds are around 10 microJ/cm2, comparable to non-water-soluble counterparts.

Abstract

Core-shell CdSe/CdS nanocrystals are a very promising material for light emitting applications. Their solution-phase synthesis is based on surface-stabilizing ligands that makes them soluble in organic solvents, like toluene or chloroform. However, solubility of these materials in water provides many advantages, such as additional process routes and easier handling. So far, solubilization of CdSe/CdS nanocrystals in water that avoids detrimental effects on the luminescent properties, poses a major challenge. This work demonstrates how core-shell CdSe/CdS quantum dot-in-rods can be transferred into water using a ligand exchange method employing mercaptopropionic acid (MPA). Key to maintaining the light-emitting properties is an enlarged CdS rod diameter, which prevents potential surface defects formed during the ligand exchange from affecting the photophysics of the dot-in-rods. Films made from water-soluble dot-in-rods show amplified spontaneous emission (ASE) with a similar threshold (130 microJ/cm2) as the pristine material (115 microJ/cm2). To demonstrate feasibility for lasing applications, self-assembled micro lasers are fabricated via the coffee-ring effect that display single-mode operation and a very low threshold of around 10 microJ/cm2. The performance of these micro lasers is enhanced by the small size of MPA ligands, enabling a high packing density of the dot-in-rods.