Quantum Effects and Size-Distributions in Anisotropic Semiconductor Clusters

Anisotropic (layered) semiconductor clusters should exhibit unique quantum properties resulting from their small dimensions in both the lateral and layer stacking direction. To probe quantum effects we synthesized clusters of Bi2S3 in the form of microcrystalline colloidal particles. Prepared at room temperature in a number of solvents the lateral dimensions of the colloidal clusters varied from 10 to 100A as measured by transmission electron microscopy and dynamic light scattering. Optical absorption spectra of the clusters reveiled a 1 to 3eV blue-shift in the band gap resulting primarily from the lateral confinement of charge carriers in the anisotropic microcrystallites. In one colloidal preparation we observed a pronounced absorption feature on the blue-shifted band edge. We believe this feature can be attributed to the increased excitonic binding energy expected in highly anisotropic semiconductor clusters.