A time-resolved fluorescence study of silicon nanoparticles: Testing the dimer stretching model

Theoretical models describing the fluorescence of silicon nanoparticles produce widely ranging absorption gaps and radiative lifetimes. To determine which calculations accurately describe the nanoparticle excited state dynamics, the fluorescence lifetimes of spherical 1.0 nm diameter silicon nanoparticles are measured over their entire range of emission energies (3.0--2.1 eV). The measured radiative lifetimes are essentially independent of emission energy. The average lifetime of 2.9 +/- 0.2 ns did not vary with temperature in the range 110--300 K. A hydrogenated structure consisting of six reconstructed silicon surface bonds showed the best agreement with these data. The presence of oxygen is considered and ruled out from comparison to absorption gap data from previous work [25].;The role of surface dimers in the fluorescence mechanism is explored using the theoretical framework of Allan, Delerue, and Lanoo [1]. Their single dimer computations are extended to a fully reconstructed structure using time dependent density functional theory. Despite the inclusion of a fully reconstructed structure and improved computational techniques, their simple stretching model produces an energy barrier inconsistent with the observed temperature-lifetime trends. The discrepancy is attributed to the neglect of more complicated dimer motions, e.g. hydrogen bond wagging.