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.

We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

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We use quantum coherence in a system consisting of one metallic nanorod and one semi-conductor quantum dot to investigate a plasmonic nanosensor capable of digital optical detection and recognition of single biological molecules. In such a sensor the adsorption of a specific molecule to the nanorod turns off the emission of the system when it interacts with an optical pulse having a certain intensity and temporal width. The proposed quantum sensors can count the number of molecules of the same type or differentiate between molecule types with digital optical signals that can be measured with high certainty. We show that these sensors are based on the ultrafast upheaval of coherent dynamics of the system and the removal of coherent blockage of energy transfer from the quantum dot to the nanorod once the adsorption process has occurred.

We study ultrafast coherent-plasmonic dynamics of hybrid systems consisting of one semiconductor quantum dot and one metallic nanoshell when they interact with a laser field with a step-like amplitude rise. It is shown that such dynamics is generated when quantum coherence in these systems can generate a retarded superenhanced local field. This process happens in the picosecond range when the applied laser field ceases to be time-dependent. We show such a field generates a strong impulse, leading to a dramatic upheaval of the collective properties of the system. These include ultrafast oscillations of the effective transition energy and linewidth of the quantum dot, and generation of a polarization pulse. Within this pulse the Förster resonance energy transfer from the quantum dot to the nanoshell happens at a significantly high rate, while after that it is blocked nearly completely. We study the collective molecular resonances of this system using Rayleigh scattering and show how the frequency of the field impulse can be tuned. The intrinsic differences between such resonances and those involving spherical metallic nanoparticles are discussed.