CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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Sample t 1 (ns) t 2 (ns) t 3 (ns) t avg (ns)
CdSe 0.5 (59%) 3.8 (34%) 17.4(7%) 2.8
CdSe/ZnTe1 0.6(65%) 3.7(18.6) 16.3(16.4%) 3.75
CdSe/ZnTe3 2.19 (41%) 18 (59%) 11.5
Table 5.1: Fits for emission decay traces for core and core shell samples
We can observe a fourfold increase of average lifetime in CdSe/ZnTe3 core-shell as
compared to CdSe core. The spatial separation of electron and hole can result in a decrease of
the wave function overlap and thus longer lifetime of charge recombination is expected in
type II heterostructures. Our observation indicates that the formation of shell leads to an
increase in lifetime which can be concluded as the clear evidence of reduced electron hole
wave function overlap in core-shell material. Furthermore present study confirms the Marcus
theory predictions which indicate an inverted regime in the present case which would in turn
indicate that the reorganization energies are very small. In case of quantum solvent seldom
plays an important role as the excitons or the charge carriers are well localized within the
bulk of the quantum dot. Therefore the nuclear reorganization energy arising from excitonphonon
coupling plays an important role in the charge recombination dynamics. To ascertain
the role of nuclear reorganization we calculate the reorganization energy and free energy
change in the case of CdSe/ZnTe3 as described by Scholes et al [5.19]. We find that the
reorganization energy, λ= 90meV and ΔG= -0.36eV. This clearly shows that for that sample
– ΔG> λ, inverted regime in terms of Marcus theory. This is also in accordance with previous
study by Scholes et al [5.19]. Such a situation arises in the case of quantum dot core shell