Purifying single photon emission from giant shell CdSe/CdS quantum dots at room temperature

TL;DR

This study demonstrates a spectral filtering technique to significantly improve single photon purity from giant shell CdSe/CdS quantum dots at room temperature by reducing biexciton emission.

Contribution

The paper reports the first observation of a large biexciton blueshift in pure-phase wurtzite quantum dots and shows how spectral filtering enhances single photon purity.

Findings

Biexciton spectrum blueshift of 24±5 nm observed in single quantum dots.

Spectral filtering reduces biexciton quantum yield by 2.3 times, improving g2(0) from 0.07 to 0.03.

Higher pump fluency further enhances purity, reducing g2(0) up to 6.6 times.

Abstract

Giant shell CdSe/CdS quantum dots are bright and flexible emitters, with near-unity quantum yield and suppressed blinking, but their single photon purity is reduced by efficient multiexcitonic emission. We report the observation, at the single dot level, of a large blueshift of the photoluminescence biexciton spectrum ($24\pm5$ nm over a sample of 32 dots) for pure-phase wurtzite quantum dots. By spectral filtering, we demonstrate a 2.3 times reduction of the biexciton quantum yield relative to the exciton emission, while preserving as much as 60% of the exciton single photon emission, thus improving the purity from $g_2(0)=0.07\pm0.01$ to $g_2(0)=0.03\pm0.01$. At larger pump fluency the spectral purification is even more effective with up to a 6.6 times reduction in $g_2(0)$, which is due to the suppression of higher order excitons and shell states experiencing even larger blueshift. Our results indicate the potential for synthesis engineered giant shell quantum dots, with further increased biexciton blueshift, for quantum optical applications requiring both high purity and brightness.