Calibrating and Controlling the Quantum Efficiency Distribution of Inhomogeneously Broadened Quantum Rods Using a Mirror Ball

TL;DR

This paper introduces a simple, cost-effective method using a silver-coated ball lens to accurately measure the full distribution of radiative and non-radiative decay rates in quantum dot nanocrystals, advancing understanding of their quantum efficiency.

Contribution

It presents a novel implementation of Drexhage's method with a ball lens to quantify inhomogeneous decay rate distributions in quantum emitters, including non-radiative processes.

Findings

Achieved accurate measurement of quantum efficiency (~0.87) in CdSe/CdS dot-in-rod emitters.

Confirmed a log-normal distribution of decay rates with a width about 30% of the mean.

Demonstrated the decay rate distribution's dependence on local optical density of states.

Abstract

We demonstrate that a simple silver coated ball lens can be used to accurately measure the entire distribution of radiative transition rates of quantum dot nanocrystals. This simple and cost-effective implementation of Drexhage's method that uses nanometer-controlled optical mode density variations near a mirror, not only allows to extract calibrated ensemble-averaged rates, but for the first time also to quantify the full inhomogeneous dispersion of radiative and non radiative decay rates across thousands of nanocrystals. We apply the technique to novel ultra-stable CdSe/CdS dot-in-rod emitters. The emitters are of large current interest due to their improved stability and reduced blinking. We retrieve a room-temperature ensemble average quantum efficiency of 0.87+-0.08 at a mean lifetime around 20 ns. We confirm a log-normal distribution of decay rates as often assumed in literature and we show that the rate distribution-width, that amounts to about 30% of the mean decay rate, is strongly dependent on the local density of optical states.