Influence of Size Purification and Self-Assembly on the Photoluminescence of Silicon Nanocrystal Ensembles

Silicon nanocrystals (SiNCs) synthesized through a nonthermal plasma reaction are purified through density-gradient ultracentrifugation in mixed organic solvents to achieve highly monodisperse fractions. These fractions show a reduction in photoluminescent (PL) linewidth, increased band alignment, and the emergence of short-range crystalline order in dried films. The films display a significant PL enhancement that we suggest arises from nanocrystal interactions in densely packed arrays and we exploit this to achieve photostable emission. We also explore how this PL enhancement emerges, from the scale of individual nanocrystals up to clusters of more than a thousand, and we examine the influence of different polymers on the self-assembly and PL stability of ensemble structures.