The stepwise self-assembly of europium sesquioxide nanocrystals into larger, anisotropic europium hydroxychloride nanostructures is observed. This involves the thermally assisted growth of 4.0 nm nanocrystals into elongated structures, called nanoneedles, and the subsequent assembly of those nanoneedles into larger, oriented bundles, called nanospindles. High-resolution transmission electron microscopy provides the size distribution, shape and atomic spacing of the nanostructures, whereas selective area electron diffraction and x-ray diffraction measurements identify their crystallinity. The optical properties, attributed to the environment of the host lattice for the europium ions, are investigated through photoluminescence measurements.

Nanometer-sized YPO₄:Eu and YVO₄:Eu particles were prepared from alkaline alcohol-water mixture with Y(NO₃)₃ 6H₂O, EuCl₃ and H₃PO₄ (or NH₄VO₄) under reflux. The resultant particles were well crystallized ranging 10-50 nm in diameter by changing reaction conditions. Europium ions in YPO₄:Eu and YVO₄:Eu was successfully reduced to Eu²⁺ ions by sodium borohydride under reflux. The peak position of blue emission due to Eu²⁺ ions (4f-5d transition) in nanocrystals was different among the materials (Y₂O₃, YVO₄ and YPO₄).

As excimer lasers extend to deep-ultraviolet and vacuum-ultraviolet wavelengths at 193nm and 157nm, optical coatings experience the challenge of eliminating possible environmental contamination, reducing scattering loss, and increasing laser irradiation durability. Wide band-gap metal fluorides become the materials of choice for the laser optics applications. In order to understand the optical properties of nanostructured fluoride films, thin GdF₃ films grown on CaF₂ (111) substrates were evaluated by variable angle spectroscopic ellipsometry. An effective medium approximation model was used to determine both the film porosity and the surface roughness. Structural evolution of the GdF₃ film was revealed with improved ellipsometric modeling, suggesting the existence of 3-layer structure, a densified bottom layer, a porous middle layer and a rough top surface. The nanostructure of the film and the surface roughness were confirmed by atomic force microscopy. The attraction of the nano-structure to environmental contamination was experimentally demonstrated.

Intramolecular photoinduced electron-transfer from a hydrazine unit to an aromatic group is studied by resonance Raman spectroscopy and electronic absorption spectroscopy. Substituted hydrazine functional groups have played an important role in studies of electron transfer reactions, photo-induced intramolecular electron transfer, and of mixed valence. A prototypical compound, 2-tert-Butyl-3-(Anthracen-9-yl)-2,3-Diazabicyclo[2.2.2]octane, that has the hydrazine to anthracene charge transfer band in a region of the visible spectrum suitable for detailed resonance Raman spectroscopy is studied in detail. Excitation profiles are obtained, calculated quantitatively by using time-dependent theoretical methods, and interpreted with the assistance of molecular orbital calculations. Excited state distortions are calculated. The largest distortions occur on the hydrazine unit; the normal mode showing the largest distortion (659 cm^-1, calculated at 665 cm^-1) involves an out of plane C-N-N-C bend consistent with removing an electron from the NN π antibonding orbital. Anthracene ring-centered CC stretches also are enhanced, consistent with populating an antibonding π orbital centered on the ring. Excellent fits to all of the excitation profiles and to the absorption band are obtained using one set of excited state potential surfaces.

We present an experimental data, which demonstrate a basically new mechanism of carrier radiative recombination in semiconductor heterostructures-recombination via Tamm-like interface states. Bright line was observed in photoluminescence spectra of periodical ZnSe/BeTe heterostructures at the energies, which correspond to the optical transitions between electron and hole Tamm-like interface states in studied heterosystem. Photoluminescence via Tamm-like interface states was observed for wide range excitation densities in the temperature range from 15K to 160K. It was found that for short-period ZnSe/BeTe heterostructures at low temperatures and at low excitation densities photoluminescence via Tamm-like interface states is much stronger than conventional interband radiative recombination.

High-performance inorganic-organic hybrid thin-film transistors (TFTs) are fabricated using semiconducting In₂O₃ thin-film deposited at room-temperature by ion-assisted deposition and thin organic dielectrics grown at near-room temperature. These hybrid TFTs combine the advantages of a high-mobility inorganic semiconductor with high-capacitance organic gate dielectrics. In₂O₃ thin-films exhibit high optical transparency in the visible region, a wide band gap, and smooth morphologies. Furthermore, the present In₂O₃ films are compatible with both inorganic dielectrics and nanoscopic high-capacitance/low-leakage organic dielectrics. The resulting transparent flexible TFTs exhibit near-1.0V operating characteristics with a very large field-effect mobility of > 100 cm²/V•s, and a near-zero threshold voltage. The high performance exhibits a significant improvement over previous organic and metal-oxide-based TFTs, and even rivals that of poly-Si TFTs. In addition, these TFTs exhibit great light- and air-stability when exposed to ambient.

We have improved charge character on the surface of phosphor particles by dispersed sub micro miter size sulfonate polystryrene beads and polyelectrolyte dispersant. The surface of TAG phosphor was analyzed with SIMS-TOF. Many hydrocarbon molecules were existed on the TAG phosphor. We could exchange the hydrocarbon into polyelectrolyte and sulfonated polystyrene beads. Characterization of the chemical bonging of polystyrene beads adhered on the surface of the TAG phosphor was archieved with x-ray photoemission spectroscopy (XPS) and FT-Raman. We could measure light efficiency of the white LED with integrating sphere spectrophotometer. Adhering sub micro miter size sulfonated polystyrene beads on the surface of TAG phosphor has enhanced extraction efficiency of light from phosphor. The sulfonated ligand and reduced difference of refractive index between phosphor and encapsulant material are responsible for the enhancement of extraction efficiency light from phosphor. Additional increase of light extraction has been observed when the phosphor particles were coated only on and near the LED chip. Surface modified phosphor particle and phosphor layer have improved LED light efficiency about ten percents.

PZT: Eu³⁺ sol-gel thin films and bulk samples were synthesized by sol-gel method. The crystalline structure (perovskite) was obtained in these materials by heat treatment at different temperatures. The temperature for the films was lower than that used in the bulk samples to obtain the perovskite-type phase. X-ray diffraction shows the presence of the perovskite phase in both kinds of materials. Emission and excitation studies of the impurity Eu³⁺ were made to determine its luminescence response. For PZT: Eu³⁺ thin films, the excitation spectra shows a broad band from charge transfer and narrow peaks due to the ⁷F₀→⁵L₆ and ⁷F₁→⁵D₃ transitions with λο=612 nm; and due to ⁷F₀→⁵L₆ and ⁷F₀→⁵D₂ with λο=650 nm. The films exhibit a PZT pyrochlore phase. The decays show two general components: a fast one and a slow one. The bulk samples do not have the PZT pyrochlore phase, but a tetragonal phase was detected. They show hypersensitive transitions as ⁷F₀→⁵D₂ (excitation) and ⁵D₀→⁷F₂ (emission). These transitions reveal the presence of Eu³⁺ in sites of low symmetry. In the bulk sample the luminescence decrease at 300 ^oC, and disappear at higher temperature. It was recovered at 1000 ^oC. Instead, the thin film recovers its luminescence at 600 ^oC. This inhibition of the luminescence could be associated wit the crystallite size formed in the samples. The PZT: Eu³⁺ thin films show several advantages in comparison to the bulk samples, as a short time of preparation, and a better perovskite phase obtained at lower temperature.

The optical properties of periodic and nonperiodic arrays of aligned multiwalled carbon nanotubes are presented. Experimental analysis indicates a complex optical response that is attributed to both the individual carbon nanotube scatterers and also to the array ensembles. These studies indicate that by controlling the geometry and spacing of the arrays, it is possible to create structures that respond very strongly to specific wavelengths or bands of wavelengths. Structures such as these may form the basis for numerous applications in energy conversion. This would include highly efficient solar energy conversion as well as sensitive, finely tuned detectors that can respond to predetermined wavelength bands ranging from the ultraviolet to the infrared region. Experimental, theoretical and modeled results are discussed as they apply to these applications. Challenges and issues are discussed.

Copper nanoparticles and microfibers have been prepared by solid state reaction using carbon nanotube (CNT) as template. Their optical and structural properties were investigated by scanning and transmission electron microscopy, X-ray diffraction (XRD), Raman scattering and photoluminescence. Carbon nanotube template was found to be the main contributor to the Raman spectra, however, after the introducing of copper, we found G band shifted to high frequency by a few wavenumbers and the shift was also related to the ratio of copper to carbon nanotube. With copper form change from nanoparticles to microfiber, the ratio of scattering intensity between D band and G band of carbon nanotube increase, which reveals a change in microcrystallinity. Compared with pure carbon nanotube, a broad photoluminescence background was found to be superimposed on the Raman spectrum of these copper related carbon nanotube, and the intensity of this photoluminescence background also increase with respect to the ratio of copper to carbon nanotube. High resolution X-ray diffraction indicated that copper lattice constant of copper fibers decreased with respect to its bulk form.

The narrow stripe selective growth of the InGaAlAs bulk waveguides and InGaAlAs MQW waveguides was first investigated. Flat and clear interfaces were obtained for the selectively grown InGaAlAs waveguides under optimized growth conditions. These selectively grown InGaAlAs waveguides were covered by specific InP layers, which can keep the waveguides from being oxidized during the fabrication of devices. PL peak wavelength shifts of 70 nm for the InGaAlAs bulk waveguides and 73 nm for the InGaAlAs MQW waveguides were obtained with a small mask stripe width varying from 0 to 40 μm, and were interpreted in considering both the migration effect from the masked region (MMR) and the lateral vapor diffusion effect (LVD). The quality of the selectively grown InGaAlAs MQW waveguides was confirmed by the PL peak intensity and the PL FWHM. Using the narrow stripe selectively grown InGaAlAs MQW waveguides, then the buried heterostructure (BH) lasers were fabricated by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good performance characteristics, with a high internal differential quantum efficiency of about 85% and an internal loss of 6.7 cm^-1.

Nanophosphors correspond to nanostructured, inorganic, insulating solid materials that emit light under particle or electromagnetic excitation. Although extensive investigation of the optical properties of nanostructured semiconductors is underway, nanophosphors remain largely unexplored. Nanophosphor Tb-doped Y₂O₃ was obtained by the solution combustion technique with Tb concentrations up to 5 at.%. Structural characterization, assessed by transmission electron microscopy and x-ray diffraction, show the existence of nanoparticles with a cubic crystallographic structure and sizes in the 30 to 70 nm range. As a result of the combustion process, the nanoparticles agglomerate into large micron-sized entities. Photoluminescence emission and excitation spectra obtained at room temperature show distinct differences in the optical behavior of the bulk and nanomaterial. Specifically, the excitation spectra of the nanophosphors are systematically blue-shifted relative to bulk spectra. The photoluminescence emission spectra, which originates from ⁵D₄→⁷F_J transitions comprising several sharp lines in the visible spectrum, also exhibit contrasting behavior upon Tb incorporation; the ⁵D₄→⁷F_5,6 intensity ratio decreases with increasing Tb content in the bulk but is constant in the nanophosphor. Finally, the maximum in the quenching curve of the nanostructured material occurs at 1.5 at %, which is three times higher than for the bulk material.

Multilayers of PbTe quantum dots embedded in SiO₂ were fabricated and characterized by means of Fourirer transform infrared and x-ray spectrometry and transmission electron microscopy. The quantum dots were grown by laser ablation of a PbTe target using the second harmonic of a Q-Switched Quantel Nd:YAG laser under high purity argon atmosphere. The glass matrix was fabricated by Plasma Enhanced Chemical Vapor Deposition using tetramethoxysilane as precursor. The reason for choosing PbTe was the absorption bands this material exhibits in the region of interest for optical communications 1.3-1.5μm making this material an excellent candidate for development of optical devices. For the glass matrix, it was studied the influence of growing parameters like RF power, distance between the RF electrodes and the total pressure in the properties of the SiO₂ films. The parameters for the PbTe ablation were assumed from a previous work. FTIR and refractive index measurements were used to estimate the best growth parameters for the dielectric host. TMOS partial pressure proved to be an important parameter to diminish the nanoparticle coalescence during the multilayer fabrication. Multilayer X-ray diffraction patterns were used to estimate the nanoparticles diameter. Morphological properties of the nanostructured material were studied using transmission electron microscopy.

Perylene tetracarboxylic diimide (PTCDI) is a material widely used in organic thin-film-based electronic and optoelectronic devices, such as transistors, light-emitting diodes and photovoltaic cells. It has been reported recently that copper phthalocyanine (CuPc) solar cell performance can be significantly improved if CuPc forms nanowires instead of flat film surface. However, nanostructures of PTCDI reported up to date include only self-assembled nanobelts in a solution, which is not suitable for small molecule device applications. For organic solar cells based on small molecules, vapor deposition organic nanostructure fabrication is of considerably more interest. In this work, fabrication of PTCDI nanostructures by evaporating PTCDI powder in Ar flow has been performed. The nanostructures were grown on glass, quartz and ITO (indium-tin oxide) substrates which were located downstream from the source. The obtained nanostructures were characterized by scanning electron microscopy (SEM) and photoluminescence (PL). The effect of substrate type, substrate temperature, gas flow rate and fabrication time on the resulting nanostructures were investigated. The synthesis conditions had significant effect on the morphologies of the resulting nanostructures, and the optimal fabrication conditions for device applications are discussed.

The purpose of this work was to investigate the optical properties of GaN nanocrystals (GaN-nc) doped by Eu³⁺ ions. The total photoluminescence excitation spectroscopy (TPLE) (where the full emission spectra were recorded for the different excitation wavelengths) has been performed to investigate the absorption properties and the energy transfer between GaN-nc and Eu³⁺ ions. Nanosized GaN:1%Eu³⁺-nc with the average grain sizes of ~ 8 nm have been synthesized as a powder by the combustion method with some modifications. In PL spectra the strong emission lines related to Eu3+ ions have been observed with the most intense line at ~614 nm. Additionally, the broad yellow/red emission band related to GaN surface/defect states has been also observed. In recorded TPLE spectra an efficient excitation energy transfer from GaN-nc to Eu³⁺ has been observed. It has been shown that there are three channels for the excitation of Eu³⁺ ions: (i) through quantized states in GaN nanocrystals, (ii) through defect-related states in the GaN, (iii) and directly through the excited states of Eu⁺³ ions. It has been found that for investigated GaN powder the most efficient is the excitation of Eu⁺3 ions through quantized states in GaN nanocrystals.

We analyze the steady state and transient properties of the polarization and of the electronic population in a triple semiconductor quantum well structure with tunneling induced interference. We first derive the dark states of the system and show that this structure can lead to double dark states. Then, we show that under the dark state conditions the system can exhibit tunneling induced transparency, slow light, transient gain without inversion and coherent population trapping. The dynamics of the polarization and of the electronic population, as well as the total trapped electronic population in the system, are found to be depended on which dark state condition is satisfied.

The tailoring of the properties of silver nanoscale structures is of great interest to fields such as nanosensing and biophotonics. Because of this, much effort is devoted to the development of new growth methods of silver nanostructures. In this work, a fabrication process for two dimensional silver structures by infiltrating self-assembled polystyrene spheres is presented. Additionally, the structural and optical characterizations of the fabricated structures are studied.