Enhanced luminescence of quantum dot/dielectric layer/metal colloid multilayer thin films

In this study, we reported the effect of the dielectric constants of the medium between quantum dots (QDs) and metal nanoparticles on the plasmon-enhanced fluorescence. The evaluation was conducted on (CdSe/ZnS)-(TiO2/SiO2)-(Au colloid) three-layer hybrid films prepared by the layer-by-layer coating. The CdSe/ZnS layer and the Au-nanoparticle layer were separated by a dielectric layer fabricated from tetraethyl orthosilicate and tetrabutyl orthotitanate. The dielectric constant of the dielectric layer was adjusted by varying the ratio of tetraethyl orthosilicate to tetrabutyl orthotitanate. We found that the optimal excitation wavelength for CdSe/ZnS QDs came with the localized surface plasmon resonance wavelength of Au colloids and could be controllable by virtue of adjusting the dielectric constant of the dielectric layer. Experimental results showed that both the optimal distance and the PL enhancement reduced with the increase of the dielectric constant. The decrease of the enhancement factor may arise from the increase of the rate of the resonant energy transfer from photo-excited CdSe/ZnS QDs to Au colloids. (C) 2013 Elsevier B.V. All rights reserved.