U. Banin et al., HOMOGENEOUS OPTICAL-PROPERTIES OF SEMICONDUCTOR NANOCRYSTALS, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 283, 1996, pp. 1-10
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.