HOMOGENEOUS OPTICAL-PROPERTIES OF SEMICONDUCTOR NANOCRYSTALS

In between the molecular and bulk forms of matter, semiconductor nanoc rystals are novel materials with interesting optical and electronic pr operties. We present a study of the homogeneous optical properties of two nanocrystal systems. First, the homogeneous absorption of InP nano crystals is studied via hole burning experiments. The optical spectrum consists of a HOMO-LUMO transition with a 10 meV width and a second e lectronic transition shifted by 0.11 eV. The optical transitions are a ssigned within a three valence-band model. The CdS/HgS/CdS quantum-dot /quantum-well system is also investigated and a transmission electron microscopy study shows that the growth of the HgS well region and the CdS outer layer is epitaxial. Selective optical techniques are used to study the electronic level structure. In hole burning, a discrete tra nsition (width of 7 meV) with pronounced phonon side bands at a freque ncy of 250 cm(-1) is observed. In fluorescence, the line narrowed spec trum also shows phonon replicas at a similar frequency. The measuremen ts provide direct evidence for charge localization in the low band gap HgS well region within this colloidally synthesized nano-heterostruct ure.