Mechanisms of Afterglow and Thermally Stimulated Luminescence in UV-irradiated InP/ZnS Quantum Dots

TL;DR

This study investigates the mechanisms behind afterglow and thermally stimulated luminescence in UV-irradiated InP/ZnS quantum dots, revealing defect-related charge recombination processes and energy trap characteristics crucial for optoelectronic applications.

Contribution

It is the first to analyze low-temperature afterglow and TSL in InP/ZnS quantum dots, providing insights into defect centers and charge trapping mechanisms.

Findings

Charge carriers recombine via defect centers involving dangling bonds.

Active traps have activation energies of 26-31 meV.

Low recapture rate of charge carriers in nanocrystals.

Abstract

Indium phosphide-based quantum dots (QDs) are a potential material for designing optoelectronic devices, owing their adjustable spectral parameters over the entire visible range, as well as their high biocompatibility and environmental safety. Concurrently, they exhibit structural defects, the rectification of which is crucial for enhancing their optical properties. The present work explores, for the first time, the low-temperature afterglow (AG) and spectrally resolved thermally stimulated luminescence (TSL) of UV-irradiated colloidal core/shell InP/ZnS QDs in the range of 7-340 K. It is shown that, when localized during irradiation and released after additional stimulation, charge carriers recombine involving defect centers based on indium and phosphorus dangling bonds. The mechanisms of the observed luminescent phenomena can be caused by both thermal activation and tunneling processes. By means of the initial rise method, the formalism of general-order kinetics, and the analytical description using the Lambert W function, we have analyzed the kinetic features of possible thermally stimulated mechanisms. We have also estimated the energy characteristics of appropriate trapping centers. A low rate of charge carriers recapture is revealed for InP/ZnS QDs. Active traps in nanocrystals of different sizes are characterized by close values of activation energy in the 26-31 meV range. The current paper discloses new horizons for exploiting TSL approaches to study the properties of local defective states in the energy structure of colloidal QDs, which can contribute to the development of targeted synthesis of nanocrystals with tunable temperature sensitivity for optoelectronic and sensor applications.