The Synthesis of Core/Shell Quantum Dots - Semiconductor Quantum Dots: Organometallic and Inorganic Synthesis - page 134

d n 1 y 4 n g | 3

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Figure 5.5 Cartoon showing charge recombination and emission in type II dots,
potential diagrams and radial wave function distributions for charge
carriers in CdTe/CdSe and CdSe/ZnTe core/shell QDs. Reprinted with
permission from S. Kim, B. Fisher, H.-J. Eisler and M. G. Bawendi,
J. Am. Chem. Soc. , 2003, 125, 11466. Copyright 2003 American
Chemical Society.

the red end of the spectrum. This means the emission can be tuned not only
by controlling the particle size, but also by carefully choosing a speci

c
core/shell structure and its dimensions. The emission radiative lifetime was
also found to be signi

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cantly longer than the simple core material, with
quantum yields of less than 4% observed. Quantum yields of up to 20% have
been obtained when a further ZnTe layer was deposited on CdTe/CdSe
particles. The low quantum yield and the unusual recombination mecha-
nism suggested the normal non-radiative pathways (such as surface states)
may be a factor to consider when examining type II materials.

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