Due to its wide band gap (3.37 eV) and large exciton binding energy (60 meV), ZnO is of great interest for photonic applications. A number of different morphologies, such as nanobelts, nanowires, tetrapod nanostructures, tubular nanostructures, hierarchical nanostructures, nanobridges, nanonails, oriented nanorod arrays, nanoneedles, nanowalls, and nanosheets, were reported. A range of synthesis methods for fabrication of ZnO nanostructures was reported as well. A common method is evaporation from mixture of ZnO and carbon, which is usually in the form of graphite. In this work, we studied the morphology of the ZnO nanostructures fabricated from the mixture of ZnO (micron-sized and nanoparticles) and carbon (graphite, single-wall carbon nanotubes). When graphite and ZnO powders were used, tetrapod structures were obtained. If one of the reactants was nanosized, the diameter of the tetrapod arms was no longer constant. Finally, when both reactants were nanosized, novel morphologies were obtained. We studied the dependence of the morphology on the amount of starting material and the type of carbon used. The ZnO nanostructures were studied using field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray diffraction. Growth mechanism and factors affecting the morphologies are discussed.

The use of semiconductor nanocrystals as a passive Q-switch in an eye-safe laser system is demonstrated. These lasers recently became popular in laser radar, three-dimensional scanning, targeting, and communication applications. Such applications require the laser to operate under Q-switching, generating a laser pulse with duration on the order of tens of nanoseconds, and a peak power on the order of a megawatt. Semiconductor nanocrystals exhibit unique physical properties, associated with the quantum size effect. The PbS and PbSe nanocrystals show a size-tunable absorption resonance in the near IR spectral region (1000-3000 nm), saturable absorbing properties, suitable as a functional Q-switch in eye-safe lasers. The quantum confinement effect and the saturable absorption can be manifested only in high quality nanocrystals with a narrow size distribution and passivated surfaces. Thus, a special synthetic procedures have been used for the preparation of PbSe core, PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed shell nanocrystals. Then, a passively Q-switched Er:glass laser has been assembled, while the laser output energy, Q-switch threshold energies, and pulse width have been measured.

We studied infrared photoluminescence in wire-like silicon crystals grown by gold stimulated CVD technique. Such crystals present the smallest Si-based heterostructure consisting of bulk silicon and a cell-assembled silicon envelope. Cells have spheroid-like shape. Size of the cells equals 2-5 nm. A thickness their fact walls is equal to ~ 1 nm. A complex structure of the crystals gives rise to a complex photoluminescence spectra consisting of the know spectra of bulk silicon ( band-exciton and LO- and TO-replicas) and intensive new band at 1,139 eV. The larger is a thickness of the envelope the more intensive new band. We studied a spectral shape of the new band and its intensity versus a power exciting and temperature. It was found that both they differ completely from the known spectra of bulk silicon and indicate on quantum origin of the envelope and on existence of superradiance.

Liquid crystal mixtures containing diacrylates and monoacrylates with carboxylic acid end groups were produced. Polymerization of the mixtures in the macroscopically oriented state led to the formation of hydrogen-bonded anisotropic networks with a high order parameter. Cadmium atoms were then incorporated in the networks and were subsequently converted to cadmium sulfide (CdS) quantum dots with a size of about 2nm using H₂S. Annealing the composites at temperatures above 80°C increased the size of the quantum dots. The composites showed strong photoluminescence with a large Stokes shift associated with defect emission. With increasing size of the quantum dots the absorption and the emission bands shifted to longer wavelengths. The formation of the quantum dots in the composite led to a large increase in the mean refractive index of the system. When the size of the quantum dots was increased further, an increase in the mean refractive index of the composite was observed.

Growth and electrochemical and optical properties of single crystalline vanadium pentoxide (V₂O₅) nanorod arrays were investigated. Vanadium pentoxide nanorod arrays were grown by electrochemical deposition, surface condensation induced by a pH change and sol electrophoretic deposition. Uniformly sized vanadium oxide nanorods with a length of about 10μm and diameters of 100 or 200nm were grown over a large area with near unidirectional alignment. TEM micrographs and electron diffraction patterns of V2O5 nanorods clearly show the single-crystalline nature of nanorods from all three growth routes with a growth direction of [010]. The growth mechanisms of single crystal vanadium pentoxide nanorods have been discussed. The transmittance of nanorod arrays decrease more quickly under applied electric field than sol-gel derived film, which suggests nanorod array electrodes possess significantly improved charge/discharge rate. Electrochemical analysis is proves that nanorod arrays have higher efficiency than sol-gel derived film. The relationships between electrochemical and optical properties, nano and microstructures, and growth mechanisms have been discussed.

Nanocrystalline ZrO2:Sm³⁺ doped at 2 mol% was prepared by sol-gel process and the structure and photoluminescence characterization as function of the annealing temperature were performed. Strong visible fluorescence emission produced by transitions ⁴G_5/2→⁴H_5/2,7/2,9/2 of Sm³⁺ was obtained by energy transfer process exciting the host at 320 nm and by direct excitation at 408 nm. The experimental results show a quenching of the emission bands by reducing the annealing temperature that is associated with a high content of tetragonal structure. Furthermore, an important change in the structure of the signal emitted was observed when ion was excited directly and the annealing temperature was reduced. These results suggest the possibility to tune the emission of ZrO₂:Sm₃₊ nanophosphor.

The water-soluble silicon quantum dots (QDs) of average diameter ~3 nm were prepared in organic solvent by ultrasound-induced solution route. This speedy rout produces the silicon QDs in the size range from 2 nm to 4 nm at room temperature and ambient pressure. The product yield of QDs was estimated to be higher than 60 % based on the initial NaSi weight. The surfaces of QDs were terminated with organic molecules including biocompatible ending groups (hydroxyl, amine and carboxyl) during simple preparation. Covalent attached molecules were characterized by FT-IR spectroscopy. These water-soluble passivation of QDs has just a little effect on the optical properties of original QDs.

In a range of nanophotonic energy harvesting materials, resonance energy transfer (RET) is the mechanism for the intermolecular and intramolecular transfer of electronic excitation following the absorption of ultraviolet/visible radiation. In the nonlinear intensity regime, suitably designed materials can exhibit two quite different types of mechanism for channeling the excitation energy to an acceptor that is optically transparent at the input frequency. Both mechanisms are associated with two-photon optical excitation - of either a single donor, or a pair of donor chromo-phores, located close to the acceptor. In the former case the mechanism is two photon resonance energy transfer, initiated by two-photon absorption at a donor, and followed by RET directly to the acceptor. The probability for fulfilling the initial conditions for this mechanism (for the donors to exhibit two-photon absorption) is enhanced at high levels of optical input. In the latter twin-donor mechanism, following initial one-photon excitations of two electronically distinct donors, energy pooling results in a collective channeling of their energy to an acceptor chromophore. This mechanism also becomes effective under high intensity conditions due to the enhanced probability of exciting donor chromophores within close proximity of each other and the acceptor. In this paper we describe the detailed balance of factors that determines the favored mechanism for these forms of optical nonlinearity, especially electronic factors. Attention is focused on dendrimeric nanostar materials with a propensity for optical nonlinearity.

Dye-sensitized solar cells (DSSC) utilizing titania (TiO₂) nanomaterials in conjunction with a light-absorbing dye have been extensively explored for the last few decades. Earlier efforts to surpass the 10% overall light conversion efficiency of these devices emphasized the synthesis of dyes with enhanced light-absorbing capabilities, but slow progress in the increase in efficiency has directed attention to the exploration into the modification of the TiO₂ nanostructure. Up to this point, the most efficient electrodes in DSSC devices have consisted of 10 micron-thick mesoporous TiO₂ film with an interconnected network of 15-20nm particles. This type of structure has shown to impart a large enough surface area for efficient light absorption and charge formation, but the random distribution of nanometer-sized particles is thought to be the limiting factor for enhanced electron transport, hindering further progress in achieving higher efficiencies. Our research utilizes TiO₂ nanorods in an attempt to explore and compare the electron transport pathways associated with 1) a random distribution of nanoparticles and 2) a straightforward arrangement of nanorods within the TiO₂ nanostructure. It is assumed that a more ordered structure of nanorods would minimize inefficient electron percolation pathways and improve ion diffusion at the TiO₂-dye-electrolyte interface by eliminating the randomization of the particle network, by increasing contact points for good electrical connection, and by decreasing small necking points that have shown to develop between adjacently-bound particles in the current TiO₂ nanoparticle structure after sintering. The current-voltage (I-V) behavior of three solar cell electrode structures consisting of (1) TiO₂ nanoparticle film, (2) TiO₂ nanoparticle-nanorod film, and (3) TiO₂ nanorod film were compared and analyzed to determine whether the nanorod structure provided a more efficient pathway for effective electron conduction. SEM analysis was also done to examine the structural alignment and morphology of each TiO₂ electrode.

Two-photon fluorescence polarisation and stimulated emission depletion dynamics are investigated in three high two-photon cross-section push-push polyenes: OM62, LP79 and OM77 and compared to the behaviour of a standard fluorophore (rhodamine 6G). Two-photon fluorescence anisotropy measurements (R(0) and Omega) were undertaken using picosecond time-correlated single photon counting (TCSPC). For OM62 and LP79 these are consistent with a diagonal two-dimensional transition tensor with S_XX>S_YY. For OM77 the contribution of off-diagonal elements (SXY & SYX) appears significant. Two-photon fluorescence anisotropy decay data is combined with streak camera measurements of excited state population depletion to determine stimulated emission cross-sections and ground state vibrational relaxation times. Cross-sections for STED in all three polyenes were found to be significantly higher than those for rhodamine 6G. The efficiency of STED is however dependent on the degree to which the S₁→S₀ transition is saturated by the DUMP pulse; this is mediated by fast ground state vibrational relaxation. Of the three polyenes, LP79 is seen to combine a large stimulated emission cross-section (c.a. 13σ(r6G)) with rapid ground state relaxation (τ_R=240fs).

Combining nonlinear optics with ellipsometry improves the information content available in studies of nonlinear optical surfaces and materials and provides a novel and general route for background suppression. As one example, this novel nonlinear optical null ellipsometry (NONE) approach allowed for the selective detection of bovine serum albumin adsorption on glass from the changes induced in the hyperpolarizability of coadsorbed rhodamine 6G, providing a general route for label-free real-time biosensing. In combination with new theoretical developments, polarization analysis in surface second harmonic generation is shown to yield rich information on molecular orientation and the optical constants of the thin surface layer. This ellipsometric technique is particularly useful in studies of chiral media, in which second-order nonlinear optical measurements have been shown to be remarkably sensitive to chirality at the interface.

Nanostructured europium-doped yttrium oxide (Y2O3:Eu) films were fabricated using electron beam evaporation, in combination with the Glancing Angle Deposition (GLAD) technique. GLAD makes use of controlled substrate motion during physical vapour deposition (PVD) of a thin film resulting in a high degree of control over the nanostructure of the film. Films were deposited using pre-doped Y2O3:Eu source material. Scanning electron microscopy was used to characterize film nanostructure, while the light emission properties of these films were characterized by photoluminescence measurements. Films of four different nanostructures were used in this study: chevrons, pillars, helices, and normally-deposited solid thin films. For each film nanostructure, measurements of the angular dependence of the intensity of the emitted light, as well as absolute brightness, were obtained and compared. The polarization of the light emitted from the chevron film was also examined using a linear polarizer to analyze the polarization state. Measurements of the selective transmission of circularly polarized light through the helical samples were obtained using variable angle spectroscopic ellipsometry.

This paper reports experimental study on the development of cadmium tungstate scintillator material in the form of nanocrystal films through controlled sol-gel processing and pre-designed doping. We chose cadmium tungstate as a base material for doping and nanostructure development due to its excellent inherent photoluminescence property. In addition, our studies revealed that doping with Li⁺, B³⁺ and Bi³⁺ resulted in appreciably reduced grain size and porosity, leading to enhanced optical transmittance. Further analyses indicated that photoluminescence output changed significantly with dopants. The relationships between doping, defects and luminescence were discussed.

We report a 94% coupling efficiency between silica waveguide (SWG) and planar photonic crystal (PPC). This is achieved using a tapered PPC with a hybrid photonic crystal structure. The hybrid structure combines triangular and rectangular crystals.

In this paper, we designed different structures for PPC tapered waveguide to enhance the coupling between silica waveguide (SWG) and planar photonic crystal (PPC). The designed structures are based on changing the radii of the inner PPC tapered waveguide's crystals before and after adding extra defects. We found that above 88% transmission efficiency is possible by using extra defects followed by radii changes. We also found that changing the operating wavelength from 1.55μm to 1.558μm increases the transmission efficiency to 90% since the field is more confined at the later wavelength.

We characterized a PMMA-quantum-dot (QD) composite fabricated by pre-polymerization of PMMA and dispersing commercially available colloidal semiconductor QDs using photoluminescence and absorption measurements. The QDs are stabilized in rapidly formed oligomer matrices, and the complete polymerization of the PMMA-QD composite is achieved by commonly used polymerization. The properties of the PMMA-QD composite are compared with the QDs in colloidal solution. Photoluminescence vs. temperature was measured from 10K to room temperature and showed a maximum value around 45K.