Presentation: 2025 ND EPSCoR Annual conference 

October 21, 2025, NDSU Memorial Union, Fargo, North Dakota

Blinking in Non-Stoichiometric CdSe Quantum Dots Governed by Thermal Fluctuations of the Surface

Semiconductor Quantum dots (QDs) are nanocrystalline structures already finding their use across a range of technological applications, including optoelectronics, lasing, biosensing, and bioimaging. Specifically, CdSe QDs have been widely investigated due to their direct band gap, size, and optical properties tunable via the shape, size, and structure-surface modifications. Although synthesis of small-size (3-6 nm) CdSe QDs frequently results in non-stoichiometric structures, it is not well studied, so far. Here, we perform ab initio non adiabatic molecular dynamics simulations on non-stoichiometric Cd28Se17Cl22 (Cd-rich) and Cd17Se28Na22 (Se-rich) to investigate how photoluminescent quantum yield (PLQY) changes with time for these non-stoichiometric clusters. In our models, Cl- and Na+ ions are used to balance the charge of the Cd-rich and Se-rich QDs, respectively. Our calculations show that at equilibrium, Cd-rich clusters are much brighter than Se-rich clusters, with PLQY values of 89% and 20%, respectively. However, thermal fluctuations significantly decrease the average PLQY for the Cd-rich cluster down to 41%, while increase it up to 36% in the Se-rich QDs. These variations arise from changes in the electron-hole localization of the lowest-energy surface-associated states, driven by shifts in the positions of surface atoms upon thermal fluctuations. We attribute this behavior to QD blinking, supporting one possible mechanism in which thermal fluctuations of surface atoms modulate the emissive states.