Ensemble brightening and enhanced quantum yield in size-purified silicon nanocrystals.
We report on the quantum yield, photoluminescence (PL) lifetime, and ensemble photoluminescent stability of highly monodisperse plasma-synthesized silicon nanocrystals (SiNCs) prepared though density-gradient ultracentrifugation in mixed organic solvents. Improved size uniformity leads to a reduction in PL line width and the emergence of entropic order in dry nanocrystal films. We find excellent agreement with the anticipated trends of quantum confinement in nanocrystalline silicon, with a solution quantum yield that is independent of nanocrystal size for the larger fractions but decreases dramatically with size for the smaller fractions. We also find a significant PL enhancement in 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.
Department of Physics and Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, North Dakota 58108, USA.
Joseph B
JB
Miller
Austin R
AR
Van Sickle
Rebecca J
RJ
Anthony
Daniel M
DM
Kroll
Uwe R
UR
Kortshagen
Erik K
EK
Hobbie
D003460:Crystallization / Q000379:methods*; D008027:Light; D008163:Luminescent Measurements; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D011789:Quantum Theory; D012542:Scattering, Radiation; D012825:Silicon / Q000737:chemistry* / Q000302:isolation & purification
D012825:Silicon