Au-silica core/shell hybrid nanoparticles furnished with CdTe nanocrystals for enhanced plasmon-exciton interactions

Abstract

To date extensive research efforts have confirmed that optical properties of bulk semiconductors and metals are substantially modified when they are transformed into nano-dimensions.1 For example, metal nanoparticles with dimensions less than hundred nanometers strongly oscillate at a specific resonance frequency to generate localized surface plasmons depending on their size. This creates strongly localized electric fields in the close proximity of the metal nanoparticles under external excitation. Similarly, because of the size effect, semiconductor quantum dot nanocrystals (NCs), with dimensions less than 10 nanometers, feature highly tunable absorption and emission characteristics. High levels of brightness and photostability, and broad excitation range with sharp emission spectra make these NCs ideal candidates as active materials in light emitting diodes and solar cells, and as fluorescent labels in bioimaging.1–4 More recently, combining these two sets of nanomaterials has received increasing attention for their possible end uses of light harvesting and light generation in optoelectronics and highly promising sensing and imaging applications in biophotonics.2–4 Even though NCs are highly amenable for such a wide range of aforementioned applications, there are still some performance related issues yet to be overcome. One of such main challenges is to increase the fluorescence quantum efficiency of NCs and other is to make them non-blinking. Plasmon coupling of NCs offers possible means to address these and similar problems. This, however, requires hybrid architectures to intimately integrate these nanomaterials. Although there are straightforward methods of simply blending these nanomaterials and making thin films of their blends, or making bilayers of these nanocrystal and metal nanoparticle films on top of each other, such methods typically suffer from either limited control in spacing metal nanoparticles and semiconductor nanocrystals precisely, or from total film thickness of bilayers that can be put together. In this work, we developed and demonstrated Au-silica core/shell nanoparticles that successfully assemble CdTe nanocrystals right on their silica shells for enhanced plasmon-exciton interactions, while avoiding the problems of lacking control in spacing and limited film thickness. Herein we present our synthesis and characterization results of this new set of CdTe NC decorated, Au-silica core/shell hybrid nanoparticles with silica shell thicknesses controlled and tuned by synthesis (Fig. 1.).