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color="#000000"><b>Seminar on</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Modern Optics and Spectroscopy</b></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><i><b>Many-body processes in colloidal semiconductor
nanocrystals</b></i></font></div>
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<div align="center"><font face="Times New Roman"
color="#000000"><b>Gautham Nair</b>, MIT</font></div>
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<div align="center"><font face="Times New Roman"
color="#000000">Tuesday, April 7, 2009</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">12:00
- 1:00 p.m.</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">To
help guide applications, the fundamental optical properties of
semiconductor nanocrystals (NCs) have been studied extensively, and
most relevant aspects of the single exciton state structure and
fluorescence are well understood. A handful of potential applications,
however, rely heavily on less understood multiexcitonic and many-body
effects. The first part of the talk will focus on carrier
multiplication (CM), the generation of more than one electron and hole
in a semiconductor after absorption of one photon. Interest in CM, a
desirable process in photovoltaic applications, has renewed in recent
years because of reports suggesting greatly increased efficiencies in
nanocrystalline materials compared to the bulk form. We will describe
our experimental assessments of CM yields in semiconductor NCs by
careful study of exciton and biexciton signatures in transient
photoluminescence decays. The CM yields we determine are much lower
than most of the reports in the literature. We discuss the
implications of our findings within a general theoretical framework.
The second part of the talk examines the role of many-body
processes in the fluorescence intermittency (blinking) of NCs. The
prevailing hypothesis for fluorescence quenching in an off NC involves
a three-body Coulomb-mediated relaxation process that is also though
to play a dominant role in the relaxation of multiexcitons in NCs. We
have studied this connection by spectrally resolving exciton and
multiexciton emission from single NCs and measuring the correlationof
their intermittency.</font></div>
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<div align="center"><font face="Times New Roman" color="#000000">Grier
Room, MIT Bldg 34-401</font></div>
<div align="center"><font face="Times New Roman"
color="#000000">Refreshments served after the lecture</font></div>
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