Understanding the Size-Dependent Photostability and Photoluminescence Intermittency of Blue-Emitting Core/Graded Alloy/Shell “giant”-Quantum Dots

Abstract

Recently, giant quantum dots (g-QDs) with a core/interface graded alloy shell/shell structure have shown promise in reducing photoluminescence (PL) intermittency and improving photostability. However, this approach has been mainly demonstrated with red and green emitting g-QDs but the blue-emitting graded alloy QDs has remained less explored. To tackle this challenge, a composition gradient method is employed to create three blue-emitting CdZnS/Cd_xZn_1–xS/ZnS core/interface graded alloy shell/shell (C/A/S) quantum dots (QDs) with different diameters. The sample with the largest diameter (gQD-3) exhibits superior optical characteristics, with a photoluminescence quantum yield (PLQY) of approximately 62% and around 80% ON/radiative events at the single-particle level. Conversely, the smallest diameter (gQD-1) sample shows lower PLQY and only 30% radiative events with longer OFF/nonradiative events. Probability distribution analysis of PL trajectories, fitted with a truncated power law, reveals a significantly higher carrier de-trapping rate in gQD-3 compared to gQD-1, attributed to its proximity to band edge trap states. Additionally, the largest diameter sample retains remarkable optical performance during 48 h of continuous UV irradiation in colloidal suspension and single-particle levels. These findings show optimized core/shell structures, gradual alloy interfaces, and outer shell coatings can stabilize blue-emitting quantum dots, advancing next-gen optoelectronics.