Stretch exponential luminescence decay of CdSe/ZnS quantum dots in colloidal solutions

Abstract

The luminescence decay of CdSe/ZnS quantum dots (QDs) coated with shells of trioctylphosphine oxide (TOPO) molecules and placed in colloidal solutions has been investigated. It is shown that the experimental luminescence kinetics is well fitted by the function \(I(t) = I_0 \exp \left[ { - \frac{t} {{2\tau _1 }} - A\left( {\frac{t} {{2\tau _1 }}} \right)^\beta } \right]\), where I0 is the initial luminescence intensity, β = 0.52 ± 0.2, τ1 = 50 ns, and constant A depends on the QD size. Time τ1 = 50 ns is interpreted as the lifetime of the QD excited state. The parameter β ≈ 0.5 indicates that the excited state is quenched via dipole-dipole energy transfer from the QD to energy acceptors (TOPO molecules and/or local bonds (C-H) in the solvent).