Time-resolved luminescence of transiently excited porous silicon reveals the dynamics of the excitation-luminescence cycle in which localized excitons efficiently generate orange-red luminescence from this material at room temperature. Upon transient excitation with nanosecond pulses, both blue and orange luminescence bands appear coincidently. At long time delays, the orange luminescence dominates. We show here that the time-delayed orange luminescence is thermally activated by hopping-related processes. The activation energy for a 500 ns delay is 36 meV. Our observations are in principle capable of resolving outstanding contradictions in the porous silicon luminescence literature. Quantum confinement on a wire fluctuating width provides the strong energy disorder which facilitates exciton localization.
- excitation dynamics
- porous silicon
- excitation-luminescence cycle