We demonstrate that an ultra-thin layer of aluminum oxide can significantly enhance the emission efficiency of colloidal quantum dots on a Si substrate. For an ensemble of single quantum dots, our results show that this super brightening process can increase the fluorescence of CdSe quantum dots, forming well-resolved spectra, while in the absence of this layer the emission remains mostly at the noise level. We demonstrate that this process can be further enhanced with irradiation of the quantum dots, suggesting a significant photo-induced fluorescence enhancement via considerable suppression of non-radiative decay channels of the quantum dots. We study the impact of the Al oxide thickness on Si and interdot interactions, and discuss the results in terms of photo-induced catalytic properties of the Al oxide and the effects of such an oxide on the Coulomb blockade responsible for suppression of photo-ionization of the quantum dots.

Published by the American Institute of Physics. Related ArticlesEffect of dimensionality and morphology on polarized photoluminescence in quantum dot-chain structures J. Appl. Phys. 112, 084314 (2012) Quasiresonant excitation of InP/InGaP quantum dots using second harmonic generated in a photonic crystal cavity Appl. Phys. Lett. 101, 161116 (2012) Size-dependent radiative decay processes in graphene quantum dots Appl. Phys. Lett. 101, 163103 (2012) Optical absorbance of doped Si quantum dots calculated by time-dependent density functional theory with partial electronic self-interaction corrections J. Chem. Phys. 137, 144301 (2012) Analysis of the modified optical properties and band structure of GaAs1−xSbx-capped InAs/GaAs quantum dotsIn this paper, we report the results of depositing CdSe/ZnS quantum dots (QDs) on Cr coated substrates. Compared to such QDs on glass surfaces, the emission peak blueshifts and broadens much more rapidly. The acceleration of the process is presented by showing the relative intensity, position, and full-width as a function of time for various laser intensities, and the effects on photoinduced fluorescence enhancement and photo-oxidiation are discussed. We also consider the thickness of the Cr layer and photo-induced heating, showing this factor should instead lead to a redshift of the peak. Oxidation of colloidal QDs is known to cause blueshifts and broadening of emission peaks (photobleaching). We attribute the faster photobleaching of QDs on Cr films to enhancement in the oxidation of the ZnS shell by catalytic or direct chemical reactions with chromium oxides. As a working hypothesis, this leads to additional paths for breakdown of the otherwise protective nature of the shell. V C 2012 American Institute of Physics. [http://dx.

Emission of semiconductor quantum dots can be increased via two fundamentally different processes: (i) surface plasmon resonances (plasmonic emission enhancement) and (ii) irradiation with light (photo-induced fluorescence enhancement). In this paper we theoretically and experimentally study the mutual impacts of these processes on each other in quantum dot solids. We show that when thin films of colloidal quantum dots are placed in the vicinity of Au nano-islands, the plasmonic enhancement of the radiative decay rates of quantum dots and Forster energy transfer can hinder the photo-induced fluorescence enhancement of these films. This in turn leads to significant suppression of their plasmonic emission enhancement when they are irradiated with a laser beam. We investigate the impact of the sizes and shapes of the metallic nanoparticles in this process and theoretically analyze how plasmons and energy transfer can hinder the electrostatic barrier responsible for photo-induced fluorescence enhancement.

We studied the impact of photophysical and photochemical processes on the interdot Forster energy transfer in monodisperse CdSe/ZnS quantum dot solids. For this, we investigated emission spectra of CdSe/ZnS quantum dot solids in the vicinity of gold metallic nanoparticles coated with chromium oxide. The metallic nanoparticles were used to enhance the rate of the energy transfer between the quantum dots, while the chromium oxide coating led to significant increase of their photo-oxidation rates. Our results showed that irradiation of such solids with a laser beam can lead to unique spectral changes, including narrowing and blue shift. We investigate these effects in terms of inhibition of the plasmonically enhanced interdot energy transfer between quantum dots via the chromium-oxide accelerated photo-oxidation process. We demonstrate this considering energy-dependent rate of the interdot energy transfer process, plasmonic effects, and the way photo-oxidation enhances non-radiative decay rates of quantum dots with different sizes.

We studied plasmonic features of bimetallic nanostructures consisting of gold nanoisland cores semi-coated with a chromium layer and explored how they influence emission of CdSe/ZnS quantum dots. We showed that, compared with chromium-covered glass substrates without the gold cores, the bimetallic nanostructures could significantly enhance the emission of the quantum dots. We studied the impact of the excitation intensity and thickness of the chromium layer on this process and utilized numerical means to identify the mechanisms behind it. Our results suggest that when the chromium layer is thin, the enhancement process is the result of the bimetallic plasmonic features of the nanostructures. As the chromium layer becomes thick, the impact of the gold cores is screened and the enhancement mostly happens mostly via the field enhancement of chromium nanoparticles in the absence of significant energy transfer from the quantum dots to these nanoparticles. V