Fluorescence enhancement in colloidal semiconductor nanocrystals by metallic nanopatterns

In this work we demonstrate the possibility of obtaining a significant increase of the photoluminescence of colloidal semiconductor nanocrystals (NCs) by means of metallic nanopatterns. Highly ordered triangular-shaped gold nanopatterns (typical dimensions 200 nm) were fabricated on planar substrates by electron beam lithography (EBL). Colloidal semiconductor nanocrystals (core/shell CdSe/ZnS quantum dots or CdSe nanorods) dispersed in a polymer matrix (PMMA) were subsequently deposited on the substrates by spin-coating. The coupling between the surface plasmons (SPs) resonance band of the metallic nanostructures and the excitation/emission bands of the nanocrystals resulted in a strong enhancement of the fluorescence from the quantum emitters, as probed by confocal microscopy analyses. Importantly, the proposed approach allows a precise control of the shape and dimensions of the single metallic nanostructure (and consequently of the SPs resonances), thanks to the nanometer resolution of the EBL. Moreover, the concentration of the NCs dispersed in the blend, as well as the thickness of the active layer, can be finely tuned. These results may open interesting perspectives for a wide range of applications, such as photonic devices, LEDs, sensor technology, microarrays, single/few molecules experiments, and biochemical/biophysical investigations.