Ensemble brightening in size purified silicon nanocrystals

We report on the quantum yield, photoluminescence (PL) lifetime and ensemble photoluminescent stability of monodisperse plasma-synthesized silicon nanocrystals (SiNCs) prepared though density-gradient ultracentrifugation in mixed organic solvents. Improved size uniformity leads to a reduction in PL linewidth, band alignment, and the emergence of entropic order in dry nanocrystal films. We find a significant PL enhancement in thin solid films assembled from the fractions, and we use a combination of measurement, simulation and modeling to link this brightening to a temporally enhanced quantum yield arising from SiNC interactions in ordered ensembles of monodisperse nanocrystals. Using an appropriate excitation scheme, we exploit this enhancement to achieve photostable emission.