Experimental and theoretical investigation of the third-order nonlinearity in CdS quantum dots in a dendrimer matrix

M. J. Potasek; Y. Gao; Michael Etienne; Roger Dorsinville; David Bauer; Valeria Balogh-Nair

doi:10.1117/12.645368

7 February 2006 Experimental and theoretical investigation of the third-order nonlinearity in CdS quantum dots in a dendrimer matrix

M. J. Potasek, Y. Gao, Michael Etienne, Roger Dorsinville, David Bauer, Valeria Balogh-Nair

Author Affiliations +

Proceedings Volume 6129, Quantum Dots, Particles, and Nanoclusters III; 61290H (2006) https://doi.org/10.1117/12.645368
Event: Integrated Optoelectronic Devices 2006, 2006, San Jose, California, United States

Abstract

We have measured the nonlinear optical response of Cadmium Sulfide quantum dots (CdS QD) in a poly(propyleneimine) dendrimer matrix having diaminobutane (DAB) core. Large refractive nonlinear coefficients and low absorption losses were observed at all wavelengths. Dendrimers are nanosize, highly branched, tree like monodisperse macromolecules that emanate from a central core with a branch occurring at each monomer unit. Dendrimers encapsulations convey stability, control of emission wavelengths by QD size. The branching points in the interior of the dendrimers are occupied by tertiary nitrogen to provide numerous nucleation sites to drive formation of QD clusters of small size. The dendrimer-stabilized CdS QDs were stable at room temperature, both in solution and in solid state for several weeks. Thin films were deposited by spin casting from methanol solutions. The resulting samples consisted of a 1mm thick quartz substrate with a 200-400 Å nonlinear optical film on one side. The Z-scan technique was used to characterize the NLO response. A mode-locked YAG laser provided the laser pulses with 30-ps duration at 355 nm, 532 nm and 1064 nm at a 20-Hz repetition rate with energies per pulse ranging from few microjoules to several millijoules. These results indicate relatively large values for the nonlinear response (> 10^-10 esu) at all three wavelengths. Our calculations indicate that quantum dot-organic systems have large optical nonlinearity due to interactions between excitons in the quantum dots and the organic medium. We calculate that an increase of the QD radius to ~4-8 nm will result in a substantial enhancement of the nonlinearity.

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M. J. Potasek, Y. Gao, Michael Etienne, Roger Dorsinville, David Bauer, and Valeria Balogh-Nair "Experimental and theoretical investigation of the third-order nonlinearity in CdS quantum dots in a dendrimer matrix", Proc. SPIE 6129, Quantum Dots, Particles, and Nanoclusters III, 61290H (7 February 2006); https://doi.org/10.1117/12.645368

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KEYWORDS

Excitons

Dendrimers

Quantum dots

Cadmium sulfide

Nonlinear optics

Absorption

Semiconductors

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