Observation of anisotropic emission from semiconductor quantum dots in nanocomposites of metal nanoparticles

Abstract

Colloidal semiconducting quantum dots ( QDs), also known as nanocrystals, offer a number of advantages in light generation, e.g., for solid-state lighting, biol ogical labeling , and bio -imaging. 3 These applications typically necessitate high quantum eff iciencies in film, preferably with polarized emission in certain applications . One of the major problems encountered when working with films of these QDs is the decrease in their fluorescence quantum efficiency in the solid for m. Another technical challenge is to obtain anis otropic emission from these QDs. Recently plasmonics has enabled a wide range of important applications related to nanocrystals including metal enhanced light generation and plasmonic biosensing.1,2 In this work, to address the se difficulties encountered with QD solids, we investigate and demonstrate anisotropic enhanced emission from semiconductor quantum dots placed in multilayered plasmon resonator nanocomposite s using strong plasmon-exciton interactions . In these metal nanoparticle (MNP) resonator architectures, we show that highly isotropic nature of QD emission c an desirably be altered through modifying emission kinetics by plasmon coupling , while also enhancing the overall QD emission. To date plasmo n coupling of such QDs has been widely studied using various methods including the self-assembly of a monolayer of QDs and a monolayer of M NPs. However, previous works studied only the plasmonic coupling of a QD film located either on top or bottom of the metal nanostructure layer , focusing on the resulting bilayer systems of MNPs and QDs . On the other hand , the emission polarization has been investigated and observed for only antisymmetric particle systems such as semiconductor nanorods. Different than th e previous reports, here our work focuses on the demonstration of plasmon -coupled QD solids in a three -dimensional construction by repeating QD -MNP unit cells to increase the quantum efficiency of the composite film and modify the isotropic emission nature of QDs in plasmonic cavities. In our bottom -up approach, the polarization properties are significantly modified , resulting in a 80% of emission in verti cal polarization, and a quantum efficiency of 30% is achieved for the se plasmonic QD-composite films. Plasmonic coupling of CdTe QD layer using Au nanoparticles in a bilayer system has been previously reported both for on-resonance 2 and off-resonance 3 spectral conditions. However , one of the most important conditions for strong plasmon-exciton interaction s is the spectral overlap between plasmon resonance wavelength of MNPs and emission wavelength of QDs. In our experiments, w e observe strong on-resonance plasmon coupling of CdTe QDs, which is also supported by o ur numerical calculation s. As depicted in Fig . 1(a)-(b) there is a significant red -shift in the localized plasmon resonance wavelength of MNPs when they are cast into a closely-packed film. In our design, w e 144 978-1-4244-5369-6/10/$26.00 ©2010 IEEE

Wavelength, Concentration, and Distance Dependence of Nonradiative Energy Transfer to a Plane of Gold Nanoparticles

“…For example, the authors reported on LSP enhancement of energy transfer between planes of QDs and in such a system quenching of the QD emission by a plane of MNPs is a competing mechanism. 21,22 Energy transfer from dyes to a nanostructured silver film, formed by the accumulation of particles of various sizes ranging from nanometers to microns, has also been recently reported. 14 Apart from its relevance to sensing and photonic device applications, by using a planar geometry the Au NP-QD separation as well as the Au NP concentration can be independently controlled.…”