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C Dots for Nanophotonics

Photonic materials have garnered interest in many fields for their promise of increasing the basic understanding of light-matter interactions as well as practical applications such as low threshold lasing, optical computing, and light emitting devices. Through the CCMR IRG Program, we are collaboratively investigating these materials with the Liddell, Gaeta and Lipson Groups here at Cornell.

Of particular interest within the field of photonic materials are bandgap materials. By their periodic structure, these types of materials confine or exclude specific wavelengths (or energies) of light. These periodic structures are on the order of the wavelength of light.

The materials used to create these structures include colloidal crystals, etched silicon and other "photonic building blocks."

One subset of these materials are so-called "active photonic building blocks" which incorporate an optically active moiety, such as an organic fluorophore. With the Liddell Group, we have developed and investigated these active photonic building blocks (incorporating C dots) and the structures produced from them.

Unfortunately, fluorophores suffer from proximity quenching and photobleaching in these situations. Proximity quenching occurs when one fluorophore is close enough to another to allow for excited state energy transfer.

Hence, organic fluorophores have an intrinsic upper limit to the concentration with which they may be incorporated in a material.         

Particles on Particles

If the organic fluorophore is encapsulated within a core-shell environment of silica, it can no longer energy transfer with its neighbors. Additionally, these small (e.g. 30nm diameter) particles may then be incorporated onto larger particles, such as ZnS spheres to make a raspberry type of structure.

In this way, the fluorescent core-shell particles may be assembled into a photonic material with no proximity quenching and lowered photobleaching, as well as improved environmental stability.

SEM

Selected References:

E. Herz, A. Burns, S. Lee, P. Sengupta, D. Bonner, H. Ow, C. Liddell, B. Baird, U. Wiesner. " Fluorescent core-shell silica nanoparticles: an alternative radiative materials platform", Proceedings of the SPIE Vol. 6096: Colloidal Quantum Dots for Biomedical Applications, 2006, 1-12

 H. Ow, D. Larson, M. Srivastava, B. Baird, W. Webb, U. Wiesner,"Bright and Stable Core-Shell Fluorescent Silica Nanoparticles", Nano Letters 5(1), 2005, 113-117

 

All images and text Copyright 2008

Wiesner Research Group - Cornell University

Image: S. Lee - Liddell Group