Long Exciton Dephasing Time and Coherent Phonon Coupling in CsPbBr$_{2}$Cl Perovskite Nanocrystals

TL;DR

This study investigates exciton dephasing and phonon interactions in CsPbBr₂Cl nanocrystals, revealing a long dephasing time and evidence of coherent phonon coupling, which are promising for optoelectronic applications.

Contribution

The paper provides the first measurement of exciton dephasing times and demonstrates coherent exciton-phonon coupling in CsPbBr₂Cl nanocrystals using advanced four-wave mixing techniques.

Findings

Exciton dephasing time of 24.5 ps at 5 K.

Homogeneous linewidth of 54 μeV.

Observation of coherent phonon coupling at 3.45 meV.

Abstract

Fully-inorganic cesium lead halide perovskite nanocrystals (NCs) have shown to exhibit outstanding optical properties such as wide spectral tunability, high quantum yield, high oscillator strength as well as blinking-free single photon emission and low spectral diffusion. Here, we report measurements of the coherent and incoherent exciton dynamics on the 100 fs to 10 ns timescale, determining dephasing and density decay rates in these NCs. The experiments are performed on CsPbBr$_{2}$Cl NCs using transient resonant three-pulse four-wave mixing (FWM) in heterodyne detection at temperatures ranging from 5 K to 50 K. We found a low-temperature exciton dephasing time of 24.5$\pm$1.0 ps, inferred from the decay of the photon-echo amplitude at 5 K, corresponding to a homogeneous linewidth (FWHM) of 54$\pm$5 {\mu}eV. Furthermore, oscillations in the photon-echo signal on a picosecond timescale are observed and attributed to coherent coupling of the exciton to a quantized phonon mode with 3.45 meV energy.