Cobalt doped zinc oxide nanostructures were prepared in room temperature through a wet chemical method. X-Ray diffraction studies confirm that the prepared particles have a hexagonal wurtzite structure. The morphology of the particles is found from Scanning Electron Microscopy. Optical absorption measurements reveal the presence of an exciton peak at 375 nm (3.31 eV). Excitation at 330 nm shows photoluminescence arising from exciton recombination and oxygen vacancies. Open aperture z-scan measurements using 5 ns laser pulses at 532 nm reveal an optical limiting behavior arising from three-photon absorption, which gets enhanced for higher concentrations of Co.

Semiconductor quantum dots [QD] have shown a great number of applications from fluorescent markers to solar cell devices. Colloidal systems have been usually obtained through chemical synthesis, that have to be devoleped for each material. The best quality QDs have been obtained with non-aqueous solution and non-physiological pH, requiring a posterior processing to be used in biology, for example. In contrast, the same physical synthetic method, such as laser ablation, would be applied to any semiconductor, metallic or dielectric material. Colloidal QD can be obtained by laser ablation of a target inside any solvent, given this method a very large flexibility. The fluorescence efficiency, however, depend on the surface traps and stability of colloids. The usual method to avoid surface traps is to grow a cap layer to passivate its surface and, at the same time, stabilize the colloid, sterically or electrostatically. In this work we report a novel technique for obtain thiol capped CdTe colloidal quantum dots in one step. A target immerse in a solution of ethanol and 3-mercaptopropyltrimethoxysilane (MPS), or thiol, was hit by a nanosecond 532 nm laser. With this assembly CdTe luminescent QDs were obtained. The colloid photoluminescence and other optical and structural properties are studied.

We present new results on single SiO₂ nanoparticles (SiO₂ NPs). NPs were obtained by full oxidation in water of silicon nanocrystals synthesized by CO₂ laser pyrolysis of SiH4. Samples of SiO₂ NPs embedded in low concentration in a thin polymer layer were prepared by spin-coating a dedicated solution on quartz cover slides. Using focused higher order laser modes, we determine the three-dimensional orientation of the nanoparticles' transition dipole moment (TDM). The SiO₂ NPs were found to possess a quite stable and randomly oriented TDM. However, characteristic dynamical effects featuring single NPs such as fluorescence intermittency and TDM flipping could also be observed. Photoluminescence (PL) spectroscopy of single SiO₂ NPs revealed spectra with a double-peak structure consisting of a narrow zero-phonon line and a broader phonon band. The phonon band can be attributed to longitudinal optical phonons excited in the SiO₂ network.

Multiple excitations in quantum dots core/shell heterostructures are studied via quasi continuous wave multiexciton spectroscopy method. For ZnTe/CdSe core/shell quantum dots, a transfer from attractive to repulsive biexciton binding energy is detected as the shell thickness increases, indicating a transfer from quasi type-I to type-II regimes. For CdSe/CdS seeded nanorods, a transfer from binding to repulsive behavior is detected for the biexciton, accompanied by significant reduction in oscillator strength of the triexciton transition as core diameters decreases below 2.8nm, indicating a transition of the electronic excited states from type-I localization in the core to a quasi type-II delocalization along the entire rod as the core diameter decreases. However, as rods dimensions are decreased, a transfer from repulsive to binding biexciton energy occurs, demonstrating a change of the system from a quasi type-II to quasi-type-I behavior.

Hydrogen and oxygen titration experiments have been performed for Au nanoparticles embedded in yttria-stabilized zirconia (Au-YSZ) nanocomposites at 500 °C and characteristic localized surface plasmon resonance (LSPR) absorption data has been acquired of the LSPR band in a variety of gas exposures. A model has been developed which attributes peak position shift to charge exchange between the gas environment and the nanocomposite. Using the calculated charge exchange, number of chemisorbed and incorporated oxygen ions, a qualitative description for the mechanisms dictating the broadening of the LSPR band have been made and the trend of the experimental data leads to the conclusion that the filled oxygen ion vacancies within the YSZ matrix for the Au-YSZ nanocomposite used in this study are at the Au nanoparticle/YSZ interface.)

Chemically synthesized colloidal quantum dots can easily be incorporated into conjugated polymer host systems allowing for novel organic/inorganic hybrid materials combining the natural advantages from both organic as well as inorganic components into one system. In order to obtain tailored optoelectronic properties a profound knowledge of the fundamental electronic energy transfer processes between the inorganic and organic parts is necessary. Previous studies have attributed the observed efficient energy transfer to a dipole-dipole coupling with Foerster-radii of about 50-70Å. Here, we report on resonant energy transfer of non-equilibrium excitons in an amorphous polyfluorene donor CdSe/ZnS core-shell nanocrystal acceptor system. By time-resolved photoluminescence (PL) spectroscopy we have investigated the PL decay behavior of the primarily excited polyfluorene as a function of temperature. We show that the transfer efficiency drops from about 30% at room temperature to around 5% at low temperature. These results shed light on the importance of temperature-activated exciton diffusion in the energy transfer process. As a consequence the exciton has to migrate very close to the surface of the quantum dot in order to accomplish the coupling. Hence, the coupling strength is much weaker than anticipated in previous work and requires treatment beyond Förster theory.

The structure of associated liquids is proposed to be described in terms of the fractal conception developed for amorphous media. The low-frequency region of Raman scattering spectrum for such liquids is shown to reflect fractal features of these media. Binary H-bonded solutions are taken to gain controlled modifications of the fractal parameters and at the same time to avoid dealing with a number of unknown variables. In particular the glycerol-water fractal parameter at certain concentration reflects the competition between different H-bond networks. This concentration corresponds to the density anomaly 40% concentration.

We discuss the compound set of two dielectric microspheres to confine light in a three dimensional region of dimensions on the order of the wavelength when the spheres are illuminated by a plane wave. This simple configuration enables the reduction of the longitudinal dimension of so called photonic jets, together with a strong focusing effect. The beam shaped in that way is suitable for applications requiring high longitudinal resolutions and/or strong peak intensities.

Nanofibers from light-emitting organic molecules such as para-phenylenes have already demonstrated a promising application potential in nanophotonic devices and can act as waveguides or nanolasers. Here, the basic mechanisms for self-assembly of three different green- and green/blue-light emitting thiophene/phenylene co-oligomers into nanofibers are investigated. Under well defined conditions in high vacuum the molecules are deposited on cleaved mica surfaces. The effect of substrate surface energy as well as epitaxy on the overall film morphology is studied and significant differences between different co-oligomers are found.

Lutetium oxyorthosilicate (Lu₂SiO₅:Ce³⁺, commonly known as LSO) is a scintillator of choice for medical imaging applications such as Positron Emission Tomography (PET) because of its high light output, high gamma ray stopping power and fast response. In the current study, phase-pure LSO ceramics were obtained with a high degree of optical transparency and excellent scintillation properties. These LSO optical ceramics were prepared by combining nanotechnology with a sinter-HIP approach. We found that the densities of the LSO ceramics increased with increasing sintering temperature, which corresponds to a systematic decrease in porosity as found by SEM examination. The residual pores were found to segregate at grain boundaries after sintering, and were essentially removed by subsequent hot isostatic pressing (HIPing), which raised the density to essentially the value characteristic of the single crystal and produced polycrystalline LSO ceramics with a high degree of transparency. Under excitation a ²²Na source such specimens displayed a light output as high as 30,100 ph/MeV. The LSO ceramics showed an energy resolution of 15% (FWHM) at 662 keV (¹³⁷Cs source) and a fast scintillation decay of 40 ns due to the 5d → 4f transition of Ce³⁺. The excellent scintillation and optical properties make LSO ceramic a promising candidate for future gamma-ray spectroscopy as well as medical imaging applications.

We studied the novel structure for improving the emission properties of semiconductor light sources both theoretically and experimentally. The proposed structure is a semiconductor pillar buried in a metal except for one end surface of the pillar. Photons are extracted only from the air-exposed surface. The structure consists of the GaAs nanopillar structures embedded in metal and is analyzed by the finite-difference-time-domain method. InAs quantum dots buried in a GaAs pillar are assumed to be the photon emitters. Simulations are performed on GaAs pillars with different diameters buried in Niobium. Consequently, the simulation showed 75% light extraction efficiency from the pillar to air with the optimization of the structure. In addition, we experimentally measured photoluminescence intensities of up to 40 times enhancement in embedded structures compared to normal pillar structure. These are promising for future applications to overcome single photon sources.

In the present study, we report the growth of silver nanoparticles in SiO2 matrix by co- sputtering technique. The effect of deposition conditions on the formation of Ag nanoparticles were systematically studied using scanning electron microscopy (SEM), UV-Vis absorption studies. The optical absorptive nonlinearity of the nanoparticles was studied by using open aperture Z- scan techniques. The surface plasmon peak in the absorption spectra indicates the presence of Ag nanoparticles in the matrix. The open aperture Z-scan studies shows the Ag- SiO2 nanocomposites can be used as a good optical limiter.

Nanogratings with chiral geometry are found to produce artificial optical activity (i.e., the ability of rotating the light polarization), though the composing materials are not optical active. This paper presents a thorough review of our recent study, from theory to experiment, on the optical activity in two types of chiral nanogratings: the dielectric gratings exhibiting the largest polarization rotation (up to 26.5°) observed to date, and the metallic ones producing simultaneous enhance transmission and enhanced optical activity. The polarization properties of the chiral gratings are demonstrated and the enhancement mechanism of optical activity due to various resonance processes are also revealed and interpreted.

Fluorescence lifetime, anisotropy and intensity dependent single molecule fluorescence correlation spectroscopy (I-FCS) are used to investigate the mechanism of fluorescence saturation in a free and nucleotide bound fluorophore (NR6104) in an antioxidising ascorbate buffer. Nucleotide attachment does not appreciably affect the fluorescence lifetime of the probe and there is a decrease in the rate of intersystem crossing relative to that of triplet state deactivation. The triplet state fraction is seen to plateau at 72% (G-attached) and 80% (free fluorophore) in agreement with these observations. Measurements of translational diffusion times show no intensity dependence for excitation intensities between 1 and 10⁵kW cm^-2 and photobleaching is therefore negligible. The dominant mechanism of fluorescence saturation is thus triplet state formation. I-FCS measurements for Rhodamine 6G in water were compared with those in the ascorbate buffer. In water the triplet fraction was saturated at considerably higher powers (45% at ca. 1.5 × 10³kW cm^-2) than in the ascorbate buffer (55%ca. 1 1kW cm^-2)

Luminescent nanoparticles are gaining more and more interest in bio-labeling and bio-imaging applications, like for example DNA microarray. This is a high-throughput technology used for detection and quantification of nucleic acid molecules and other ones of biological interest. The analysis is resulting by specific hybridization between probe sequences deposited in array and a target ss-DNA usually expressed by PCR and functionalized by a fluorescent dye. These organic labels have well known disadvantages like photobleaching and limited sensitivity. Quantum dots may be used as alternatives, but they present troubles like blinking, toxicity and excitation wavelengths out of the usual range of commercial instruments, lowering their efficiency. Therefore in this work we investigate a different strategy, based on the use of inorganic silica nanospheres incorporating standard luminescent dyes or rare earth doped nanocrystals. In the first case it is possible to obtain a high luminescence emission signal, due to the high number of dye molecules that can be accommodated into each nanoparticle, reduced photobleaching and environmental protection of the dye molecules thanks to the encapsulation in the silica matrix. In the second case, rare earths exhibit narrow emission bands (easy identification), large Stokes shifts (efficient discrimination of excitation and emission) and long luminescence lifetimes (possibility to perform time-delayed analysis) which can be efficiently used for the improvement of signal to noise ratio. The synthesis and characterization of good luminescent silica spheres either by organic dye-doping or by rare-earth-doping are investigated and reported. Moreover, their application in the DNA microarray technology in comparison to the use of standard molecular fluorophores or commercial quantum dots is discussed. The cheap and easy synthesis of these luminescent particles, the stability in water, the surface functionalization and bio-compatibility makes them very promising for present and future applications in bio-labeling and bio-imaging.

Amorphous and nanocrystalline ZnO thin films were synthesized by the sol-gel process at room temperature. The films were spin-coated on glass and silicon wafers and gelled in humid air. The ZnO films were synthesized by using zinc acetate dihydrate as the inorganic precursor. The samples were annealed at at 450°C for 15 minutes to produce a polycrystalline ZnO thin films. The films were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electronic microscopy and UV-Vis absorption spectroscopy. The experimental absorption spectrum of the crystalline ZnO film exhibits an absorption band located at 359 nm. Emission and excitation studies of the ZnO nanocrystallites were made in both kinds of materials to determine its luminescence response. Photoconductivity studies were performed on amorphous and crystalline (wurtzite phase) films. The experimental data were fitted with straight lines at darkness and under illumination at 355 nm and 633 nm. This indicates an ohmic behavior. Transport parameters were calculated. Results are discussed.

A new and promising approach for the design and fabrication of novel optical devices is the functionalization of individual pores in 2D photonic crystals (PhC). This can be done by infiltrating the pores with polymers or dyes. We present a method to locally infiltrate individual pores. This new technique enables the fabrication of a new class of devices, such as optical switches or multiplexers. For the infiltration of individual pores 2D PhC templates made of macroporous silicon were used. Local addressing of the pores is carried out by using focused ion beam technology. For the infiltration itself the wetting assisted templating process is applied. We will present experimentally the infiltration of different polymers and different optical designs.

A laser induced thermal lens technique has been employed to evaluate the dynamic thermal parameter, the thermal diffusivity, of gold nanofluids. Gold nanoparticles were synthesized by citrate reduction of HAuCl₄ in water. The UVVIS optical absorption spectra show an absorption peak around 540 nm owing to surface Plasmon resonance band of the gold particles. The thermal diffusivity of gold nanoparticles was evaluated by knowing the time constant of transient thermal lens obtained by fitting the experimental curve to the theoretical model of the mode-matched thermal lens. Analyses of the results show that the nanofluid exhibits lower thermal diffusivity value in comparison to the host medium, water. Further investigations also reveal that the concentration of nanoparticles in the fluid have influence on the measured thermal diffusivity value. Results are interpreted in terms of interfacial thermal resistance around the nanoparticles as well as on the clustering of nanoparticles.

We have investigated a numerical stability of transfer matrix method for the calculations of transmission spectra in 1D photonic structures based on ionic crystals. Transfer matrix method was found to lead in appearance of some non-physical peaks in the calculated transmission spectra for some values of the number of layers.

Nanocrystalline TiO₂ films doped with gold nanoparticles were synthesized by the sol-gel process at room temperature. The TiO₂ films were synthesized by using tetrabutyl orthotitanate as the inorganic precursor. The films were spin-coated on glass wafers. The samples were annealed at 100°C for 30 minutes and sintered at 520°C for 1 hour to generated anatase and rutile phases. The films were characterized using UV-Vis absorption spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. An absorption peak located at around 651 nm is due to the surface plasmon resonance of the gold nanoparticles. Optical absorption spectrum was fitted by Gans model by using a high refractive index (n_local = 2.6). This high index is related to the high content of anatase nanoparticles embedded in the film. Photoconductivity studies were performed on nanocrystalline (anatase phase) films. The experimental data were fitted with straight lines at darkness and under illumination at 515 nm and 645 nm. This indicates an ohmic behavior. Transport parameters were calculated. Results are discussed.

The thiol-ene reaction is a established photoreaction of multifunctional thiols and enes. Virtually any type of ene will participate in a free radical polymerisation process with a thiol. An advantage over many other photochemical reactions is that the reaction proceeds almost as rapidly in ambient conditions as in inert atmosphere. In this work we introduce the UV-crosslinking of polynorbornenes made by ring opening metathesis polymerization making use of the residual double bond in the polymer backbone. The crosslinking experiments were done in thin films and were followed by FTIR measurements, to proof the accessibility of double-bonds in the polymers for the addition of the thiols. As a result of these pre-experiments we created flexible and light transmitting films. To further increase the scope of this reaction, amphiphilic block copolymers were prepared and used to form block copolymer micelles in a selective solvent, which were subsequently crosslinked with pentaerythritol tetra(3-mercaptopropionate) (PETMP). FT-IR, DLS and SEM-measurements were used to prove the successful crosslinking and thus nanoparticle formation.