Proton Irradiation Effects on Colloidal InGaP/ZnS Core-Shell Quantum Dots Embedded in Polydimethylsiloxane: Discriminating Core from Shell Radiation-Induced Defects through Time-Resolved Photoluminescence Analysis

In scintillation and dosimetry applications, the increasing interest on the use of colloidal quantum dots (QDs) in comparison with organic fluorophores is mainly due to their easier chemical processability, narrower photoluminescence (PL) emission, and higher cross-section for ionizing radiation. The development of scintillators and dosimeter based on QDs, however, relies on a deep understanding of the effects of ionizing radiation on QD structures. In this paper, we present the optical characterization of colloidal cadmium-free InGaP/ZnS core-shell QDs embedded in polydimethylsiloxane (PDMS) and irradiated with 2 MeV protons (H+) in the fluence range of 1014 to 1015 H+ cm-2. Steady-state PL measurements of the irradiated samples show a decrease of the average QD PL intensity, indicating the introduction of PL quenching centers. Time-resolved PL measurements, acquired with a time-correlated single photon counting system, provide a way to probe the radiation-induced change in the carrier recombination dynamics of the QDs. A detailed analysis of the time-resolved PL curves demonstrates the presence of PL quenching defects localized both at the inner (core) and at the outer (shell) structure of the nanocrystal. The radiation-induced change in the QD optical properties, coupled with a suitable radiation hardness of the PDMS in these irradiation conditions, open the way for possible future applications related to dosimetry systems based on QDs as nanostructured sensing elements.