LETTER pubs.acs.org/JPCL
Photoluminescence of Individual Au/CdSe Nanocrystal Complexes with Variable Interparticle Distances Xuedan Ma,† Katharyn Fletcher,† Tobias Kipp,† Marcin P. Grzelczak,‡ Zhe Wang,† Andres Guerrero-Martínez,‡ Isabel Pastoriza-Santos,‡ Andreas Kornowski,† Luis M. Liz-Marzan,‡ and Alf Mews*,† † ‡
Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany Departamento de Química Física, Universidade de Vigo, 36310 Vigo, Spain ABSTRACT: We investigate the photoluminescence behavior of individual CdSe nanocrystals attached to silica-coated Au nanoparticles. These hybrid nanostructures show enhanced photoluminescence intensity, suppressed off-states, as well as shorter lifetimes in comparison with the isolated CdSe nanocrystals. The very same investigated hybrid nanostructures are further relocated by transmission electron microscopy to study the corresponding structures and geometries. Correlating the optical and structural properties of the hybrid nanostructures, we find that the lifetime shortening of the CdSe nanocrystals depends on the distance between the CdSe nanocrystals and the Au nanoparticles. The results are compared with theoretical calculations based on the FDTD method and the GerstenNitzan model. SECTION: Nanoparticles and Nanostructures
B
y taking advantage of the surface plasmons excited in metallic nanostructures and the appealing optical properties of semiconductor nanocrystals (NCs), metalNC hybrid nanostructures have attracted much attention over the past decade because of their various potential applications.1,2 The presence of neighboring metallic nanostructures influences the photoluminescence (PL) properties of NCs mainly in two ways. First, the excitation rates of the NCs are altered because of the variation of local electromagnetic field caused by surface plasmons in the metallic nanostructures. Second, the decay rates of the NCs, including both the radiative and nonradiative rates, are also changed. Competition between these factors can lead to either PL enhancement38 or quenching912 of the NCs, depending on the detailed conditions. Because of the complexity of the interaction, different factors, including composition, size, and geometry of the metallic nanostructures, as well as distance and spectral overlap between the NCs and the metallic nanostructures, influence the overall PL behavior of the NCs. For understanding fully and exploiting the interaction between NCs and metallic nanostructures, the investigation of individual NCs from a well-defined hybrid nanostructure of nontrivial shape and geometry, especially with rationally designed distance and particle size ratio between the NCs and the metallic nanostructures, is essential. So far, many studies with various types of metallic nanostructures have been performed at the single NC level.36,8,9,11 However, detailed knowledge of the hybrid nanostructure geometries in the vicinity of the investigated individual NCs somehow remains ambiguous, which makes precise simulation extremely difficult. In this work, we attempt to get a closer picture of the influence of metallic nanostructures on the neighboring NCs. Therefore, r 2011 American Chemical Society
photophysical properties of individual NCs measured by means of a confocal scanning microscope were directly correlated with the corresponding structures and geometries of the very same hybrid nanostructures measured with transmission electron microscopy (TEM). The experimental results were then compared with theoretical calculations. This experimental approach is expected to be useful for selective designs of hybrid complexes as well as for examination of various theoretical models. The metallic nanostructures we used were quasispherical Au nanoparticles (AuNPs) with an average diameter of 55 ( 5 nm, synthesized following the method reported in ref 13. To adjust the distance between the NCs and the AuNPs, we grew a homogeneous silica shell with a thickness
