<!doctype html public "-//W3C//DTD W3 HTML//EN">
<html><head><style type="text/css"><!--
blockquote, dl, ul, ol, li { padding-top: 0 ; padding-bottom: 0 }
--></style><title>March 6, 2007</title></head><body>
<div><font face="Arial" color="#000000">Seminar on<br>
<b>Modern Optics and Spectroscopy<br>
<br>
<br>
Moungi Bawendi</b>, MIT<br>
<br>
<i><b>Nanocrystal quantum dot science and technology: The
importance of spectroscopy<br>
<br>
</b></i>March 6, 2007<br>
<br>
12:00 - 1:00 p.m.</font></div>
<div><font face="Arial" color="#000000">Grier Room 34-401<br>
</font></div>
<div><font face="Times New Roman" color="#000000">This talk will
review the background chemistry and photophysics of nanocrystal
quantum dots that is relevant to their application in opto-electronic
devices and biomedical and biological imaging. We will begin by
discussing the spectroscopy of excitons and multiexcitons in single
quantum dots. Most device applications of quantum dots thus far
involve either the generation of excitons followed by light emission,
such as in a light emitting device, or the generation of excitons
followed by exciton ionization and harvesting of carriers, such as in
a photoconductive device or a solar cell. Multiexciton physics in
quantum dots is important for potential lasing applications and for
probing the possibility of carrier multiplication from quantum dots,
which has been proposed as a route to increasing the efficiency of
quantum dot based solar cells. We will report on the use of
correlation spectroscopy to unambiguously determine multiexciton
emission. We will also assess carrier multiplication in CdSe quantum
dots. We will give an overview of photoconduction in quantum dot films
and the parameters that describe and modify its efficiency. Finally,
we will give examples of the application of quantum dots as the
emitters in layered hybrid inorganic/organic light emitting devices
and in devices where the charge transport layers are inorganic oxides.
For biological imaging and biomedical imaging, we will show that
quantum dots can be engineered to be more than passive reporters of
their location; that they can also act as sensors of their
microenvironment. We will provide an example of a quantum dot based pH
sensor that is ratiometric and self-referencing and that is optimized
for the biological environment.</font></div>
</body>
</html>