This PDF file contains the front matter associated with SPIE Proceedings Volume 9161, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We present an improved and efficient numerical method to determine the optical properties of nanostructures starting from the electronic properties. We study the variation of electronic and optical properties induced by confinement effects in semiconductors quantum objects. We solve the time-independent Schrödinger equation with a new formulation of a shooting method under the effective mass approximation. This formulation is adapted to quantum wells, circular cross-section quantum wires and spherical quantum dots. We applied a correction on the mass to take into account the nonparabolicity of the band structure. The correction gives an accuracy comparable to more demanding calculation methods such as 8-bands k•p, tight binding or even semi-empirical pseudopotential methods. Our results remain valid even for low-bandgap materials and sizes as small as 1 nm. The calculation speed of our method allows optimization procedures that give better understanding of experimental results concerning CdS, CdSe, PbS and PbSe spherical quantum dots. We consider extensive data from the literature. We focus on the relations between the electronic structure and absorption and photoluminescence spectra measured on spin-coated PMMA thin-films containing (core)shell nanoparticles.

Semiconductor quantum dots possess attractive optical properties useful in the photonic field. Thanks to the evolution of core-shell colloidal synthesis, quantum dots exhibit almost ideal emitting properties. Their employment in optoelectronic devices is encouraged by their size-tunable emission as well as by their high absorption cross-section and high photoluminescence quantum yield. In this work, starting from the archetypal CdSe based system, the influence of shell thickness and composition on exciton dynamics in CdSe/Cd_xZn1_-xS core-shell QDs is investigated. By means of steadystate and transient optical spectroscopy, single- and multi-exciton recombination processes are characterized and correlated with different shell materials. The present study clarifies why graded CdSe-CdS-Cd0.5Zn0.5-ZnS core-shell represents the best performing heterostructure for optical gain applications, since such quantum dots combine the high radiative rates of CdS with the superior confinement potential of ZnS in a single dot.

Surface plasmon resonance (SPR) is one of the main mechanisms of Surface Raman Enhance Scattering (SERS) and it will depend on the morphology and free carrier density of substrates, in many of discussions have been proved. Recently, the semiconductor copper(I) sulphide (Cu2S), the natural p-type semiconductor, exhibits remarkable SPR in the nearinfrared region^[1] and can be regards as best candidate for active SERS substrates. In this report, the successive ionic layer adsorption and reaction (SILAR) process will be used to synthesis Cu₂S nanostructures^[2] from ZnO nanorods as template deposited by electrochemical reaction. To further manipulate the different carrier densities of Cu₂S nanostructuress, the adjustment of Cu vacancy in Cu₂S can be accomplished by thermal processes under noble gas. Taking 4-aminothiophenol (4-ATP) as probe molecule to measure the SERS performance by Cu₂S nanostructures made in this fabrication and also examines the effect on SERS by adjusting Cu vacancy under an excited wavelength of 632.8 nm and light power of 15 mW. In fact, the modulation of Cu vacancy will positively correlate to the SPR frequencies and so could get the best enhancement factor under the limited condition of excited source. Therefore, our results could provide a new opportunity to use SERS to explore the molecule-semiconductor interaction, a fundamental but essential question for designing novel devices.

We performed Finite Difference Time Domain (FDTD) calculation to investigate the enhancement of optical properties such as light scattering and absorption of Au-hybridized TiO₂ core-shell structures which can lead to the improvement of photocatalytic and solar cell performance. The results showed that by hybridization of Au as core and TiO₂ as shell provides the significant enhancement of light scattering and absorption. Furthermore, the tuning of scattering resonance wavelength may be achieved by varying the diameter of Au core. Our result suggests that hybridization Au and TiO₂, with proper introduction of interband states in TiO₂, can increase and color-tune the photocatalytic efficiency and solar cell performance of TiO₂ nanostructures.

Engineered organic-inorganic hybrid materials, HyMat, offer new opportunities for the easy, fast and cheap development of miniaturized functional devices. The integration of inorganic oxide networks, organic functional groups and optically active molecules or nanoparticles allows to obtain combinations of properties and structures otherwise impossible with traditional materials.

In particular, a simple and highly versatile synthesis platform enabling preparation of HyMat is presented, which is built up by a bottom-up sol-gel approach at low processing temperatures. A few types of key building blocks pave the way for accessing HyMat and make up their formulation, providing a means to synthesize innovative materials enabling to get:

- optically active micro and nanostructures;

- miniaturized sensors for analytes in gaseous or liquid media;

- direct patternability with a range of lithographic techniques;

- variable inorganic and organic compositions, and controlled porosity.

Examples of micro and nanostructures based on these spin-on materials with ceramic (i.e. SiO₂, GeO₂, Al₂O₃, ZrO₂, TiO₂,) and hybrid compositions will be presented for different applications including plasmonic or fluorescent sensors, dry-etching masks with outstanding resistance, optically active micro and nanostructured platforms and high resolution patterns.

In this paper we present our recent research results in synthesizing various metal oxide nanoparticles for use as laser gain media (solid state as well as fiber lasers) and transparent ceramic windows via two separate techniques, co-precipitation and flame spray pyrolysis. The nanoparticles were pressed into ceramic discs that exhibited optical transmission approaching the theoretical limit and showed very high optical-to-optical lasing slope efficiency. We have also synthesized sesquioxide nanoparticles using a Flame Spray Pyrolysis (FSP) technique that leads to the synthesis of a metastable phase of sesquioxide which allows fabricating excellent optical quality transparent windows with very fine grain sizes. Finally, we present our research in the synthesis of rare earth doped boehmite nanoparticles where the rareearth ion is encased in a cage of aluminum and oxygen to prevent ion-ion proximity and energy transfer. The preforms have been drawn into fibers exhibiting long lifetimes and high laser efficiencies.

One of the critical challenges for achieving solar-to-hydrogen efficiency greater than 10% (100 W/m²), especially in metal oxide photoelectrodes, is the poor internal quantum efficiency arising from high, bulk and surface, recombination and insufficient light absorption. Plasmonic light harvesting has emerged as a promising strategy to address this challenge. However, most designs are photocatalyst specific and employ precious metals, making large scale applications infeasible. We present metal-photocatalyst core-shell and semiconductor-metal-photocatalyst coremultishell nanowires as a novel class of multi-functional plasmonic photoelectrodes. By combining the optical resonances with the localized surface plasmon resonance within the proposed structures, we achieve extreme light absorption in the visible range within ultrathin photocatalyst layers. Such enhanced absorption ensures that the photocharges are preferentially generated very close to the photocatalyst-electrolyte interface and can effectively drive the reaction forward, thereby improving the internal quantum efficiency. Specifically, for nanowires in an aqueous electrolyte, we demonstrate the effectiveness of aluminum and copper to confine light and establish them as plasmonic alternatives to precious metal counterparts such as silver and gold therefore enabling cheap and scalable plasmonics. Further, we probe the absorption as a function of the permittivity of the electrolyte and show that the absorption in such nanowires is large even for high permittivity electrolytes. Hematite and copper(I) oxide have been chosen as the test materials to validate the generality of this approach. Notably, for hematite, we show that aluminum is more effective than copper, while for a broadband absorber such as copper(I) oxide, we show that both aluminum and copper are equally effective for plasmonic light harvesting.

We propose multiple resonances in the thin profiled dielectric films. The excitation of the dielectric resonances results in giant electric and magnetic field fluctuations. We observe dielectric enhanced Raman scattering in the investigated dielectric films.

We demonstrate that the refractive indices of important functional metal oxides (TiO2, SnO2, and ZnO) can be engineered “at will” for applications in photonics engineering. The tailoring of the refractive indices is accomplished by 3D nanostructuring in the sub-wavelength regime (50nm or less) using the method of block-copolymer templating combined with a low cost solution processing approach. Using this method, the index of refraction of the demonstrated metal oxides and their doped variants can be engineered to be as low as 1.25. We will present both numerical simulations and experimental data demonstrating the unrestricted integration of functional metal oxides with a D-shaped optical fiber for applications in chemical and biological sensing. Using the developed refractive index engineering scheme, we introduce a novel hydrogen sensor by integrating a palladium doped TiO₂ nanomaterial with D-shaped optical fiber and provide sensor characterization up to 700°C for applications in the energy sector.

Transparent polymers are extensively used in everyday life, from windows to computer displays, from food packaging to lenses. A possible approach for modulating their optical properties (refractive index, transparency, color and luminescence) is to change the chemical structure of the polymer, however this option is in many cases economically prohibitive. Our approach, instead, relies in the use of standard polymers with the supplement of specific nanostructured additives able to tune the final property of the material. Among others, the cases of luminescent solar concentrators based on poly(methylmethacrylate) containing luminescent quantum dots and highly transparent polymer nanocomposites with high refractive index will be presented.

In this work, the angular light output enhancements of LEDs were investigated from the spontaneous emission and light scattering of devices with different photonic crystal (PhC) geometries. The emitted photon coupled into a leaky mode is differentiated by the manipulation of the quality factor in various spatial frequencies. Therefore, light extraction in this light-emitting device is determined by the modal extraction lengths and the quality factor obtained from the measured photonic bands. Furthermore, the higher- and lower-order mode spontaneous emissions are affected by the nonradiative process in the PhC structures with different periods. In our cases, the photonic crystal device with the largest period of 500 nm exhibits the highest lower-order mode extraction and quality factor. As a result, a self-collimation behavior toward the surface-normal is demonstrated in the 3D far-field pattern of such a device. We conclude that, with the coherent light scattering from the PhC region, the spontaneous emission of the material and spatial behavior of the extracted mode can be both managed by the proper design of the device.

We exploit the unique properties of electromagnetic waves in nanophotonic structures to enhance the capabilities for active control of electromagnetic thermal transfer at nanoscale. We show that the near-field thermal transfer between two nanospheres can exhibit thermal rectification effect with very high contrast, and with large operating bandwidth. In this system, the scale invariance properties of the resonance modes result in a large difference in the coupling constants between relevant modes in the forward and reverse scenarios. Such a difference in coupling constants provides a new mechanism for thermal rectification.

Heating processes in plasmonics are essential every time the interaction with electromagnetic fields induces dissipation within metallic nanostructures. In particular the capability to predict the final temperature reached by a system (e.g. an ensemble of nanoparticles within a host medium) can be crucial when dealing with electronic, medical or chemical applications. Here we present a dispersive model of the dielectric function of a metallic medium which depends on temperature. Since temperature, in turn, depends on the intensity of the electromagnetic source and on the optical response of the medium itself, the model expresses non-linearity features. The model, which does not require any fitting parameter, can be utilized whenever the impact of temperature on the optical response of a system needs to be clarified and/ or when non-linearities might play a major role.

Rare earths in confined systems are studied because their possible imaging applications. In this work we studied the optical properties of Eu³⁺ inside nanoporous spheres. Their properties were compared with these from europium in solid SiO₂ spheres prepared by sol-gel method. Nanoporus channels were produced by using a surfactant. The last one was removed by chemical procedure. Then, europium was incorporated into the channels. XRD reveals the hexagonal structure of the pores. That was confirmed by HRTEM that shows the channels, clearly. N2 adsorption- desorption isotherm Type IV, characteristic of mesoporous materials, was obtained by BET. The I(⁵D₀→⁷F₂)/I(⁵D₀→⁷F₁) asymmetry ratio from Eu³⁺ transitions was obtained by photoluminescence. It had a value of 2.65 in the solid spheres and 1.65 in the nanoporous ones. That means Eu³⁺ is in an asymmetric site in both systems, and asymmetry is bigger in the solid spheres. Because the differences, we can use this parameter to distinguish between both systems, easily. Photoluminescence lifetimes were obtained for the ⁵D0 → ⁷F₂ emission. It was shorter in the solid spheres than in the nanoporous ones, confirming there is a more asymmetric site for the rare earth in the first case. IR spectra shows Eu³⁺ is not incorporated as part of the SiO₂ network.

This work is focused on examining ultrafast photoluminescent properties of InAs quantum dots (QDs) grown on GaAs substrate and covered by GaAs_1-xSb_x strain reducing capping layer (SRL). The samples were prepared by Stranski-Krastanow growth method. The aim is to understand the processes occurring inside the QDs and wetting layer (WL) and how the SRL influences the energy levels inside the QDs. It was already proven that the SRL of this composition can decrease energies of transitions inside these QDs to the IR range, which makes these structures promising candidate for devices emitting near infrared radiation. It is possible to shift the luminescence wavelength towards 1.3 and even 1.55 μm, which are widely used in telecommunications. Using upconversion method we measured luminescence dynamics of two samples with different concentration of Sb in the SRL with sub-picosecond time resolution. We investigated the effect of temperature, as well as the intensity and wavelength of the excitation pulse. We also compared the properties of the samples after excitation by λ=760 nm pulse and 850 nm pulse – the former one is energetically above the GaAs substrate band gap; in the second case we excited only the QDs and the WL. We consequently derived recombination and relaxation processes occurring inside InAs QDs and also proved that the transport of charge carriers from the substrate and from the WL into the QDs is efficient.

Compact description of far-field optical interactions between plasmonic nanocomposites and adjacent media permits facile a priori design of devices for light manipulation. Limited tractability of nanoscale descriptions at device-architectures previously limited development of plasmonic devices. Optical interactions between nanocomposites and adjacent optical elements, a simple device, are describable using infinite linear algebraic sums. Influence of plasmonic absorption and non-linear phenomena on device performance are distinguishable from measured transmission, reflection, and attenuation (resonant and non-resonant losses) of nanocomposites featuring nanoparticles in multiple dimensions. Two- and threedimensional distributions of gold nanoparticles supported by silica and poly(dimethylsiloxane) substrates, respectively, are considered. A unique ternary map of transmission, reflection, and attenuation correlates far-field optical behavior to nanoparticle density and opacity of the adjacent element. Intuitive, visual specification of nanoparticle density and adjacent media needed to obtain a desired optical behavior is possible using the ternary map. The compact model and ternary map provide useful tools for the design and integration of plasmonic nanocomposites into photonic devices for sustainable energy and biomedical applications.

This work proposes a novel white light device consisted of a yttrium aluminum garnet (YAG) phosphor-doped zinc oxide (ZnO) (ZnO:YAG) thin film deposited on a indium tin oxide (ITO) glass substrate by ultrasonic spray pyrolysis. Characteristics of the ZnO:YAG (YAG at 1, 5, and 10 wt%) film on ITO glass substrates were examined by x-ray diffraction (XRD) pattern, hall measurement, and photoluminescence (PL) pattern spectra. The color of the PL spectra of the yttrium-aluminum garnet (YAG) phosphor-doped zinc oxide (ZnO) thin films under excitation of He-Cd laser with wavelength of 325 nm is nearly white.

Transparent conducting indiuim galium zinc oxide (IGZO) films were successfully grown on glass substrates at room temperature by rf magnetron sputtering. Structural, optical, morphological and electrical properties of IGZO films deposited at different rf power were investigated. Composition of the film was analysed by EDAX measurement which shows that percentage of Zn increased with the rf power. Surface morphology of the IGZO film measured from AFM analysis showed that the roughness of the film was increased with increase in RF power. The average transmission in the visible range was greater than 80% and the transmission in the higher wavelength region decreased with increase in RF power. The carrier concentration in IGZO films could be controlled by controlling rf power due to the increase of Zn/(Ga+In+Zn) ratio. Nonlinear properties of IGZO thin films were measured using z-scan technique. Increase in free electron concentration of IGZO thin films lead to a decrease of the corresponding nonlinear optical absorption response.