In this contribution we explored the impact of irradiation intensity on the fluorescence of single quantum dots and ensembles of single quantum dots over time scales much greater than the blinking of the individual quantum dots. We also investigated how blinking and photo enhancement are influenced by photo-oxidation when the intensity of the irradiating laser was increased. Analysis of the emission photographs shows the presence of large time scale individual and ensemble blinking behavior. Analysis of the data indicates that photoinduced fluorescence enhancement occurs even when the inter-dot spacing of the quantum dots precludes the formation of a Coulomb blockade. Additionally, irradiation of ensembles of CdSe/ZnS SQDs at higher source intensities lead to a more accelerated suppression of quantum dots emission via photo-oxidation than for ensembles of closely packed quantum dots.

Record-brightness infrared LEDs based on colloidal quantum-dots have been achieved through control of the spacing between adjacent quantum-dots. By tuning the size of quantum-dots, the emission wavelengths can be tuned between 900nm and 1650nm.

The photoprotection of Chlorophyll-a (Chla) is important for its utilization in light harvesting assemblies. Photodegradation effects seen in the Chla solution appear to be inhibited due to the incorporation of Au nanoparticles. The protecting ability of Chla by AuNPs is the result of their efficient binding with Chla at its nitrogen sites even in dark, thus, inhibiting the reaction of reactive oxygen species with Chla, known to cause its degradation during illumination.

We report on light-sensitive nanocrystal skin (LS-NS) platforms composed of monolayer visible nanocrystals (NCs) on top of bilayers of polyelectrolyte polymers. These LS-NS devices are operated on the principle of photogenerated potential buildup, unlike common photodetectors that operate on the basis of charge collection. The resulting devices are as highly sensitive as common photosensors, despite utilizing a monolayer of NCs and requiring no applied external bias. In this device architecture, using only a single NC monolayer also allows to reduce noise current generation. This LS-NS platform is highly stable under ambient conditions with fully sealed NC monolayer, promising for low-cost large-area UV/visible sensing applications. However, such visible NC based LS-NS devices exhibit limited performance in the long wavelength range due to the low optical absorption of these NCs (e.g., CdTe NCs) in this spectral range. Here, to enhance the device sensitivity, incorporating silver nanoparticles into LS-NS is proposed and demonstrated. For that, the optical absorption of CdTe monolayer NCs in the LS-NS devices is increased using the embedded silver nanostructures. With plasmon coupling, we observe a 2.6-fold enhancement factor in the photosensitivity around the localized surface plasmonic resonance peak of the nanostructures. Higher sensitivity improvement is also obtained at longer wavelengths. To predict the enhancement in the sensitivity of the LS-NS, numerical simulations are performed and the simulation results are found to agree well with the experimental data. Plasmonically enhanced LS-NS hold great promise for large-area photosensing applications extending from UV to IR including windows and facades of smart buildings.

Two growth techniques - antimony exposure and graded growth, were proposed to achieve the control over the morphology and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures. By exposing the surface of InGaAs buffer layer to trimethylantimony precursor before the growth of InAsSb nanostructures, the surface/interface energy in the system is reduced, while the strain energy in the system is enhanced. This leads to a change of island shape from dot structure to wire structure. By using a higher initial mole fraction of trimethylantimony precursor during the graded growth of InAsSb, more Sb can be incorporated into the InAsSb islands despite the same Sb mole fraction averaged over the graded growth. This also results in a shape change from dot to wire structure. As a result of their shape change, photoluminescence from the InAsSb nanostructures shows different polarization characteristics.

We performed a thorough investigation of mid-infrared heavy-to-light hole intersubband absorption in the valence band of p-doped GaAs quantum wells with AlAs barriers. For the p-type doping a high-purity solid carbon source was used. The experimental results are compared with theoretical simulations. The inclusion of layer inter-diffusion well reproduces the transition energies. We estimate a 6-10 Å inter-diffusion length that is consistent with electron microscopy measurements. A careful analysis of our results provides valuable information for further design of emitters and detectors based on hole intersubband transitions in the valence band.

We theoretically show when single hybrid systems consisting of a metallic nanoparticle and a semiconductor quantum dot interact with a coherent light source (a laser field), quantum coherence in the quantum dot can dramatically influence the plasmonic field of the metallic nanoparticle. As a result, the quantum dot can self-renormalize the plasmonic field that it experiences. Using this we show when the applied laser field has a step-like amplitude rise, the effective field experienced by the quantum dot can exhibit strong oscillations with significantly high amplitudes for a short period of time. Our results also reveal the correlation between this effect and the Rabi flopping induced by plasmonic effects when a quantum dot is in the vicinity of a metallic nanoparticle. These results suggest that in a quantum dot-metallic nanoparticle system quantum coherence not only can change the magnitude of the field that the quantum dot experiences, but also, compared to the applied field, it can significantly increase the rate of its time variations. The results suggest that quantum dot-metallic nanoparticle systems can be appealing host for investigation of quantum plasmonic effects and photonic-plasmonic devices.

Silver (Ag) nanoparticles dispersed in an amorphous silica (SiO2) matrix or coated by a SiO2 layer were synthesized by flame spray pyrolysis (FSP). The coated nanoparticles were produced by using a modified enclosed FSP setup, in which the SiO2 precursor was injected through a ring above the FSP nozzle at various burner-ring-distances (BRDs), after the core Ag nanoparticles had been formed. The produced nanoparticles were characterized by XRD, BET, TEM and UV/vis analysis. The Ag particle size was possible to be controlled by tuning the FSP parameters. For the SiO2 coated nanoparticles, larger Ag core sizes were obtained for higher BRDs. All the produced nanoparticles exhibited the characteristic plasmon resonance frequency of Ag nanoparticles.

We devise an experiment, variable pulse rate photoluminescence, to control the accumulation of charges and the activation of charge traps in colloidal nanocrystals. The dynamics of these states is studied, with pulse repetition frequencies ranging from a few hundred hertz to the megahertz regime, by monitoring photoluminescence spectrograms with picosecond temporal resolution. We find that both photocharging and charge trapping contribute to photoluminescence quenching, and both processes can be reversibly induced by light.

We report a systematic study of polarization and magnetic field effects on the optical response of Fe3O4-silicone elastomer composite. The Fe3O4 particles were aligned in a silicone elastomer matrix with an external static magnetic field. Films of composites containing 5wt% of 20nm ≤ d ≤ 30nm Fe3O4 particles aligned in- and out-of-plane in the elastomer host were prepared. The optical spectra of the films were measured with the Perkin-Elmer Lambda 950 UV/vis/NIR spectrometer. We observed a systematic redshift in the optical response of the outof-plane composite films with increasing static magnetic field strength, which saturated near 600 Gauss. We obtained a maximum redshift of ∼46 nm at 600 Gauss. The observed redshift in the optical response of the out-of-plane composite film is attributed to the effect of the magnetic field. This facilitated the formation of the highly aligned particles that induced strong electric dipole in the aligned particles. Interestingly, there were no observable shifts with increasing magnetic field strength in the in-plane films, suggesting that the orientation (polarization) of the magnetic dipole and the induced electric dipole play a crucial role in the optical response.

Bio-silica nanostructures from diatoms (called frustules) featuring plasmonic gold nanoparticles (NPs) are elaborated using two methods based on plasma sputtering of gold. The first investigated method uses a thermal treatment to induce the thermal dewetting of a plasma sputtered gold layer on the diatom frustules. The second method first consists of coating the frustules with polyethylene glycol before sputtering gold on these frustules. For both methods, the amount of gold appears to be a key parameter regarding the final obtained layer, which can either be nanostructured by cavities or consist in individual gold NPs. For an amount of sputtered gold equivalent to form a 5 nm thick layer, both methods allow obtaining diatom frustules covered by gold NPs with a size around 20 nm and a narrow size distribution. The UV-visible characterization of the diatom frustules featuring gold NPs highlights a plasmon extinction band in agreement with individual gold NPs with a size below 25 nm.

Ultraviolet (UV) photoconductivity in pure ZnO thin films and metal (Ag, Au, Pt) nanoparticles (NPs) dispersed on ZnO thin films based UV photodetectors biased at 5 V for ultra violet radiation of λ = 365 nm and intensity = 24 µwatt/cm2 has been studied. All the three metal (Ag, Au, Pt) NPs synthesized by Polyol process when dispersed on the surface of 100 nm thin ZnO film results in enhanced photoconductive gain (K) in comparison to pure ZnO (3.1×103). An increase of about an order in K has been obtained in the case of Ag NPs/ZnO and Au NPs/ZnO UV photodetectors ( K = 6.9×104 and 5.3×104 respectively). On the other hand, Pt NPs enhance K by about two orders (5.0×105). Such an enhanced photoconductive gain has been achieved due to the lowering of dark current after dispersing the metal NPs on the surface of ZnO and increased photocurrent upon UV illumination. This may be attributed to the plasmon propagating property in metal NPs which enhances the light trapping through optical absorption in ZnO thin film surface (high photo current).

Zinc oxide (ZnO) nanoparticles and nanoparticles of luminescent zinc oxide (ZnO:Zn) phosphor were successfully synthesised and well characterised. A transparent polystyrene composite sheet containing ZnO:Zn nanoparticles was prepared by a solvent casting method. The sheet manifested comparable transmission to a virgin polystyrene film due to very uniform dispersion of the ZnO:Zn nanoparticles into the polystyrene. Evidence for uniform dispersion was evident in both its luminescent properties and in a SEM image. The photoluminescent characteristics of the ZnO:Zn, both as a pure powder and embedded in a polystyrene matrix, are reported. The uniformity of the photoluminescence of the composite sheet under near ultraviolet excitation is demonstrated. The luminescent ZnO:Zn nanoparticles are shown to have applications for use not only as an inhibitor of the ultraviolet degradation of polymers, but also for providing polymers with light emitting functionality.

Gold (Au) nanoparticles were synthesized and deposited on the perovskite SrTiO3 (STO) via a one-step solution plasma sputter deposition (SPSD) without any reducing reagents at ambient condition. Good dispersion of the Au nanoparticles deposited on the STO surface was clearly observed. The synthesized Au nanoparticles were well-crystallized with a spherical shape and preferably exhibited multiply twinned structure. An average diameter of Au nanoparicles was estimated to be 6.1 ± 1.4 nm by transmission electron microscopy. Enhanced photocatalytic activity was found for the Au-STO when compared to the pure STO, as investigated from the degradation of methylene blue solution under ultraviolet and visible light irradiation. The SPSD seems to be a rapid and facile approach to prepare the Au nanoparticles supported on the metal oxide for photocatalytic applications.

We study the mutual effects of photoinduced processes (irradiation effects) and plasmonic emission enhancement in close-packed CdSe/ZnS colloidal quantum dots in the vicinity of gold metallic nanoparticles with two significantly different size distributions. For this we examine the impact of the heat generated by the metallic nanoparticles, the strength of plasmonic field enhancement, and the rate of energy transfer from the quantum dots to metallic nanoparticles in the presence of a laser field with low and moderate intensities. Our results show that the interplay between the photophysics of the quantum dots and their plasmonic emission enhancement is significantly pronounced when the metallic nanoparticles are large. In such a case we observed large suppression of photoinduced fluorescence enhancement (PFE). For smaller metallic nanoparticles the results suggest mostly an overall time-independent suppression of the quantum dots’ emission with no significant impact on PFE.

The objective of this study was to assess usability of silver nanoparticles loaded on amorphous carbon (Ag-C) hollow nanospheres for the removal of Methylene Blue (MB) molecules from aqueous solutions. Using microwave technique, silver nanoparticles of different weight ratio was deposited onto amorphous carbon templates. The carbon hollow spheres were derived from glucose using hydrothermal technique. Interestingly crystallite size of Ag decreased with the silver loading on carbon nanospheres. Using UV-vis spectroscopy, the kinetics of MB removal from the solution was assessed. The degradation of MB followed pseudo-first-order kinetics. The obtained results showed that Ag-C particles are efficient MB degradation agent with the rate constant as high as 0.19 m-1 under visible light and 0.041 m -1 under UV light. Thus Ag-C particles are good alternative as low-cost scavenger of dye molecules in wastewater treatments.

CdS:Li nanoparticles were grown by the thermolysis method using a surfactant to control the nanoparticles growth and the passivity of the dangling bonds. The effect of the Li incorporation on the optical and structural properties of the CdS nanoparticles was studied by means of the optical transmission, photoluminescence, X-ray diffraction and HR-SEM&TEM techniques. The optical energy band gap lies in the interval from 2.7 to 3.6 eV. The photoluminescence spectra present a band with peak at 465 nm, which is indicative of the quantum confinement. The energy peak position (465 nm) is blue-shifted respect to the bulk material (512 nm). Then, one can infer that the energy band gap and the peak intensity vary according to the nominal lithium concentration in the growth solution. An average crystallite size of about 5 nm was estimated by the Brus equation and the Debye-Scherrer formula, and confirm by HR-SEM&TEM measurements.