Activation energy distribution in thermal quenching of exciton and defect-related photoluminescence of InP/ZnS quantum dots

TL;DR

This study investigates the temperature-dependent photoluminescence quenching in InP/ZnS quantum dots, proposing a band model with Gaussian-distributed activation energies to explain exciton and defect-related emission behaviors.

Contribution

The paper introduces a quantitative band model with Gaussian distribution of activation energies to analyze thermal quenching in InP/ZnS quantum dots, linking size distribution to energy level spread.

Findings

Size distribution correlates with activation energy scatter.

Electron escape from the core is the main non-radiative mechanism.

Defect-related emission quenching involves hole center emptying.

Abstract

Thermal quenching is one of the essential factors in reducing the efficiency of radiative processes in luminophores of various nature. The emission activity of low dimensional structures is influenced also by multiplicity of parameters that are related to synthesis processes, treatment regimes, etc. In the present work, we have investigated the temperature dependence of photoluminescence caused by exciton and defect-related transitions in ensembles of biocompatible InP/ZnS core/shell nanocrystals with an average size of 2.1 and 2.3 nm. The spread in the positions of energy levels is shown to be due to size distribution of quantum dots in the ensembles under study. For a quantitative analysis of the experimental data, we have proposed a band model accounting for the Gaussian distribution of the thermally activated barriers in the photoluminescence quenching processes. The model offers the thermal escape of an electrons from the core into the shell as the main mechanism for non-radiative decay of excitons. In turn, the quenching of defect-related emission is predominantly brought about through the emptying of the hole capture centers based on dangling phosphorus bonds. We have revealed the correlation between size distributions of quantum dots and scatter of the activation energy of exciton luminescence quenching. The developed approach will give further the possibility to optimize technological regimes and methods for band engineering of indium phosphide-based type-I quantum dots.