Size quantization in small semiconductor particles

Optical effects due to size quantization in three dimensions have been observed for CdS and PbS colloids with particle diameters less than 50 A and 20 to 200 Å, respectively. The optical absorption edge is blue shifted ∼0.9 eV for the CdS colloid; for PbS colloids the shift is ∼2 eV for particle diameters 20-30 Å, and ∼1 eV for particle diameters 50-200 Å. The results are consistent with perturbation of the semiconductor band structure due to carrier confinement resulting in an increase in the effective band gap.