Iwan Moreels
Physics and Chemistry of Nanostructures
Ghent University
Krijgslaan 281 – S3
Gent, Belgium
iwan.moreels@ugent.be
The Absorbance and Luminescence Properties of Colloidal Lead Salt Quantum Dots
A wealth of information on the effects of quantum confinement in colloidal quantum dots
(Qdots) can be obtained from a simple measurement of the absorbance spectrum of a Qdot
suspension. Using PbS and PbSe Qdots, I will present how the Maxwell-Garnett effective
medium theory can be applied to obtain the Qdot absorption coefficient µ. From µ, the
oscillator strength of the band gap transition is derived. Experimental results are in excellent
agreement with theoretical tight-binding calculations. I will also show that µ can be
extrapolated to short wavelengths using bulk semiconductor data. A Kramers-Krönig analysis
then yields the Qdot complex dielectric function ε. This quantity gives access to important
practical data such as the Qdot refractive index n and the static dielectric constant. In addition,
it yields further insight in the effects of quantum confinement on the Qdot optical properties.
Next, I will focus on the luminescence properties of colloidal lead salt Qdots. For practical
applications, Qdots must often be processed into thin films. We can do this via LangmuirBlodgett (LB) deposition, which yields a monolayer of Qdots on both flat and patterned
substrates. The luminescence of PbS, PbSe and PbSe/CdSe core/shell Qdots will be compared
before and after deposition. In suspension, all Qdots are expected to be highly luminescent,
yet in LB films only the PbS Qdots retain their brightness.