Optical Behavior of Single and Clustered Colloidal Semiconductor Quantum Dots Analyzed with an Integrated Fluorescence Confocal Microscope

 

Hyeonggon Kang1, Leonard F. Pease2, Silvia H. De Paoli Lacerda3, Matthew L. Clarke1, Jack F. Douglas3, Alamgir Karim3, and Jeeseong Hwang1

 

1 Optical Technology Division, National Institute of Standards and Technology

2 Process Measurements Divison, National Institute of Standards and Technology

   Department of Chemical Engineering, University of Utah, Salt Lake city, Utah.

3 Polymers Division, National Institute of Standards and Technology

 

As colloidal semiconducting Quantum dots (QDs) have increasingly been employed in diverse areas, a thorough understanding of the optical characteristics of single QDs has become important. In the applications of nanotechnologies employing unique optical properties of QDs, recent reports have described intriguing results that the optical characteristics of clusters of several (one, two, or three) QDs are quite different from those of single QDs.  Understanding the details of these differences and the fundamental mechanism on how they are different has become essential in the application of QDs for quantitative technologies such as optical assessment of nano assembly and molecular optical imaging where QDs are used to specifically label dilute or concentrated targets. However, the comparative research between single and clusters of QDs is extremely challenging, especially when the clusters include only several QDs, because it is hard to control the exact number of QDs in a cluster in a reproducible manner. Here, we report our success in preferentially producing groups of monomers, dimers, or trimers of CdSe/ZnS QDs on different substrates using the differential mobility analysis (DMA) technique. Dimers and trimers were formed by non-covalent self assembly reaction in a salt solution. These samples were analyzed with a home built integrated confocal microscope capable of simultaneous fluorescence emission lifetime, fluorescence spectrum, and fluorescence intermittency measurements. These results are compared with the same set of optical characteristics measured from labyrinthine QDs of CdSe where multiple single crystal grains are physically connected to a larger multi-crystal structure. The dynamical optical properties of these labyrinthine QDs are strikingly different from those of monomer QDs while they exhibit some common characteristics of those of clusters of QDs. We will also discuss potential mechanisms to explain dynamical optical characteristics of nanoscale systems in this report.  

 

 

 

Author information:

 

Name     :      Hyeonggon Kang

Mentor   :      Jeeseong Hwang

Division :      Optical Technology Division

Bldg/Room:  216/B217

Mail stop:     8443        

Phone :         301-975-8547

Fax :             301-975-6991

E-mail :        hyeong.kang@nist.gov

Sigma Xi :   No

Poster Category :  Materials Science