CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

184
CHAPTER 7
Summary and Outlook
7.1. Thesis Summary
The premise of the thesis is to better understand carrier dynamics in QD based
nanostructures. In the present thesis we have investigated dynamics in TiO 2 and II-VI QD
nanostructures. The dynamics investigated in most cases include cooling, trapping and
recombination of carriers. Synthesis of QD nanostructures is a major part of the present
thesis. The synthesized QDs were characterized by X-Ray diffraction, transmission electron
microscopy, electron diffraction, optical techniques etc. Charge carrier dynamics were
studied by time correlated single photon counting and ultrafast transient absorption
spectroscopy. Details of the studies carried out in the present thesis are described in chapters
3-6. The conclusion formed out of these studies is described below.
Focus of the work described in chapter 3 is on effect of particle size on interfacial
electron transfer dynamics from alizarin to TiO 2 . Alizarin binds strongly to TiO 2 surface and
has been shown to sensitize TiO 2 . The binding of alizarin leads to broadening of absorption
of TiO 2 which indicated a strong covalent interaction. On photoexcitation with 400nm,
alizarin transfers electron to TiO 2 conduction band. The electron transfer dynamics was
compared to bulk TiO 2 as control. Electron injection was found to be multiexponential
injection in contrast to monoexponential ultrafast injection in bulk TiO 2 . Aggregation and
multilayer formation as the reason for observation of multiple injection components were
ruled out as concentration of the dyes was low. Multiexponential injection components were