Nonradiative decay of singlet excitons in cadmium selenide nanoparticles

Nonradiative decay of excitons is a competing process to Multi-Exciton Generation (MEG) in nanoparticles. Nonradiative decay of single excitons with sufficient energy to generate bi-excitons in Cd₂₀ Se₁₉ and Cd₈₃ Se₈₁ nanoparticles was studied using Tully's Molecular Dynamics with Quantum Transitions (MDQT) method and a CdSe pseudopo- tential. Exciton decay rates increase with increases in nanoparticle temperature and density of lower-lying excitonic states. There did not appear a significant effect of size on energy decay rates. The decay dynamics generally follow a gradual decay with transitions between nearby states. This is punctuated by periodic, short-lived periods of rapid downhill tran- sitions that result in a large proportion of excess exciton energy being transferred to the vibrational motion of the nanoparticle. The time for relaxation to below the 2.0E[subscript g] cutoff was on the order of 1ps.