[MOS] March 6, 2007

[Zina Queen]

Seminar on
Modern Optics and Spectroscopy


Moungi Bawendi, MIT

Nanocrystal quantum dot science and technology:  The importance of spectroscopy

March 6, 2007

12:00 - 1:00 p.m.
Grier Room 34-401

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.
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