Jaebeom Lee1, Nicholas A. Kotov1, Alexander O. Govorov2, T Javed2, T Skeini2, and G. W. Bryant3. (1) University of Michigan, 2300 Hayward, HH Dow Building #3074, Ann Arbor, MI 49109, (2) Ohio University, Department of Physics and Astronomy, Athens, OH 45701, (3) Quantum Processes and Metrology Group Atomic Physics Division, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8423, Gaithersburg, MD 20899-8423
A superstructure made from Au and Ag nanoparticles (NPs) and CdTe nanowires (NWs) connected by biological affinity pair demonstrated two to five-fold enhancement of NW luminescence. The mechanism of emission enhancement in these two different types of NP-NW conjugates is drastically different even though the final optical properites are similar. In the Au NP assemblies, the energies of exciton in CdTe and plasmon in Au NP coincided and enhancement of the fluorescence originated from exciton-plasmon resonance. However, for the assemblies with Ag NPs, the emission enhancement comes from the increase in the efficiency of light absorption caused by the collective electrical field generated by Ag NPs surrounding the NW. This conclusion is made considering that (1) the plasmon peak of Ag NPs does not overlap CdTe emission; (2) calculations of collective plasmon excitations in the Ag-NP shell demonstrate the enhancement of the electrical field in the band of CdTe adsorption; and, (3) excitation spectra match very well the theoretical data. This work demonstrates a new optical process in Ag-based NP-NW superstructures, which can also take place in other metamaterials made from metal and semiconductor nanoparticles. As well, the NP-NW assemblies with stimulated absorption can serve as a conceptual foundation for a variety of optoelectronic devices including detectors/sensors with enhanced sensitivity and solar energy converters.