This PDF contains the front matter associated with SPIE Proceedings Volume 6639, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Recently there are many reports on the nonlinear optical (NLO) and electronics properties of semiconducting binary nanocrystals such as CdSe, PbS and CdS. In the spectral regime where the photon energy (ħω) is less than the bandgap (E_g), two photon absorption and two-photon-absorption-associated processes are dominant mechanisms. When ħω > E_g, however, saturable absorption due to band filling mechanism plays an important role. However, very few results related to optoelectronics properties on ternary nanocrystals are reported. Here, we present large NLO properties of ternary nanocrystals such as AgInS₂ quantum dots (QDs) and AgInSe₂ nanorods (NRs) studied by femtosecond laser pulse at 780 nm. By employing Z-scan and transient absorption techniques, the third-order susceptibility of AgInS₂ QDs and AgInSe2 NRs has been measured to be as large as 10^-8 esu. The origin of NLO properties in AgInS₂ QDs is due to two photon absorption. While the NLO behavior of AgInSe₂ NRs is mainly contributed by saturation in the nonlinear absorption and optical Kerr nonlinearity with a recovery time determined to be a few ten picoseconds.

Optical characteristics of microcavity organic light-emitting devices (OLEDs) having two mirrors are examined. Analyses show that a high-reflection back mirror and a low-loss high-reflection exit mirror are essential for such microcavity devices to obtain luminance enhancement relative to conventional noncavity devices. The capping layer in the composite mirror plays the role of enhancing reflection and reducing absorption loss, rather than enhancing transmission. In addition, by setting the normal-direction resonant wavelength around the peak wavelength of the intrinsic emission, one obtains the highest luminance enhancement along the normal direction and hardly detectable color shift with viewing angles, yet accompanied by highly directed emission and lower external quantum efficiency. On the other hand, the highest enhancement in external quantum efficiencies and the most uniform brightness distribution are obtained by setting the normal-direction resonant wavelength 20-40 nm longer than the peak wavelength of the intrinsic emission, yet with noticeable color shift over viewing angles. Due to the tradeoffs between different emission characteristics in choosing the resonant wavelength, the exact design of microcavity devices would depend on actual applications.

GaN nanowires have been the subject of intense research lately, due to the many potential ultraviolet applications and interesting properties that they possess. Because GaN has an anisotropic wurtzite crystal structure, many of its properties are dependent upon crystal orientation. For example, the photoluminescence (PL) of GaN nanowires with growth direction along the a-axis is blue-shifted relative to the PL of wires with growth direction along the c-axis. However, the origin of the difference in PL between nanowire samples of different growth directions remains unclear. To determine if surface states play a role in the dependence of GaN nanowire photoluminescence on crystal orientation, we use time-integrated photoluminescence (TIPL) and time-resolved photoluminescence (TRPL) to study the PL from GaN nanowire samples of different crystallographic orientations. We observe temporal dynamics of the blue-shifted PL feature in the a-axis GaN nanowires that is suggestive of a surface trapping process occurring, where some fraction of electron-hole pairs are prevented from recombining via the band edge emission process because carriers diffuse to the surface where they are trapped before carrier relaxation to the band edge is complete. Once a carrier is trapped and localized at a surface trap state, light emission primarily occurs only when the complementary carrier diffuses to the same surface trap. We envision that a thin oxide layer forming at the surface introduces surface traps that cause the blue emission, and that the surfaces of the a-axis GaN nanowires are more susceptible to this oxidation than the c-axis GaN nanowire surfaces.

Zinc Oxide (ZnO) photonic crystals (PCs) are of great interest in recent years due to its potential applications in optoelectronic devices. However, most of the growth temperatures in fabricating ZnO nanostructures in periodic structures reported up to date are very high (>500°C), which is not favorable for low cost manufacture. In this work, a method involving low growth temperature (90°C), hydrothermal synthesis, was used to fabricate ZnO nanostructures. Self-assembly of polystyrene (PS) spheres was used to fabricate periodic arrays. PS spheres were self-assembled on the silicon (Si) or fluorine-doped tin oxide (FTO) substrate with ZnO seed layer derived from zinc acetate. After crosslinking the PS sphere layer, hydrothermal growth was performed. The influence of growth conditions (concentration, addition of PEI, etc.) on fabricated ZnO nanorod array has been studied. Then, PS spheres were removed by annealing in air, and fabricated ZnO nanorod arrays were studied by scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. Periodicity of the array was strongly substrate dependent (better on Si than on FTO). Light emitting diodes were also fabricated in order to demonstrate the potential use of this ZnO periodic array.

Stable, OH free zinc oxide (ZnO) nanoparticles were synthesized by hydrothermal method by varying the growth temperature and concentration of the precursors. The formation of ZnO nanoparticles were confirmed by x-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies. The average particle size have been found to be about 7-24 nm and the compositional analysis is done with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Diffuse reflectance spectroscopy (DRS) results shows that the band gap of ZnO nanoparticles is blue shifted with decrease in particle size. Photoluminescence properties of ZnO nanoparticles at room temperature were studied and the green photoluminescent emission from ZnO nanoparticles can originate from the oxygen vacancy or ZnO interstitial related defects.

The Photoluminescence (PL), FFTIR, Raman characterization, XRD and TEM of Er doped nanocrystals (Y₃Al₅O₁₂:Er) prepared by glycolate method modified with PVA and UREA is reported. Irregular morphology was observed but for some concentration of PVA and UREA nanorods was observed, being PVA dominant in final morphology. XRD patterns show the presence of hexagonal phase of YAG (YAH) when the UREA was used but pure YAG crystalline structure was obtained with only PVA. Raman spectroscopy confirms the crystalline phase and in combination with infrared spectroscopy the presence of oxygen deficiency was observed. Strong green emission was observed as a result of the upconversion mechanism due to the two photon process. Luminescence results show that both PVA and UREA do not modify the emission properties but control the morphology.

Optically transparent nanostructured SiO₂ glassceramics containing a high density of monodispersed nanometer-sized clusters of semiconducting SnO₂ have been obtained by phase separation from a sol-gel derived synthesis. Complex impedance spectroscopy analysis has been performed to get information about the conduction mechanisms to understand the electrical behavior of the material. Measurements have been taken with applied bias ranging from +40 V to -40 V and with an alternated voltage signal in the range 20 Hz - 1 MHz and amplitude from 10 mV to 300 mV. An equivalent circuit, based on a metal-oxide-semiconductor model, comprising nanostructuring contributions, allows measurements fitting. Capacity-voltage and conductance-voltage curves have been obtained for each component.

Devices based on optical technology for high speed communication networks require materials with large nonlinear optical response in the ultrafast regime. Nonlinear optical materials have also attracted wide attention as potential candidates for the protection of optical sensors and eyes while handling lasers. Optical limiters have a constant transmittance at low input influence and a decrease in transmittance at higher fluences and are based on a variety of mechanisms such as nonlinear refraction, nonlinear scattering, multiphoton absorption and free carrier absorption. As we go from bulk to nanosized materials especially in the strong quantum confinement regime where radius of the nanoparticle is less than the bulk exciton Bohr radius, the optical nonlinearity is enhanced due to quantum confinement effect. This paper is on the ultrafast nonresonant nonlinearity in free standing films of PbS quantum dots stabilized in a synthetic glue matrix by a simple chemical route which provides flexibility of processing in a variety of physical forms. Optical absorption spectrum shows significant blue shift from the bulk absorption onset indicating strong quantum confinement. PbS quantumdots of mean size 3.3nm are characterized by X-ray diffraction and transmission electron microscopy. The mechanism of nonlinear absorption giving rise to optical limiting is probed using open z-scan technique with laser pulses of 150 fs pulse duration at 780 nm and the results are presented in the nonresonant femtosecond regime. Irradiance dependence on nonlinear absorption are discussed.

The thermoluminescence (TL) characterization of undoped and Lu³⁺ doped nanocrystalline ZrO₂ under β-ray irradiation is presented. The average crystallite size was 40 nm and the crystalline structure was monoclinic although for doped samples 5 wt% of tetragonal was observed. The TL results show a typical second order kinetic with four TL peaks centered around 120, 170, 240 and 280 °C when the sample is exposed to β-ray irradiation. The presence of dopant ion induces changes in the trapping process and recombination efficiency in the TL response. The result is that dominant peak typically centered at 120 °C was quenched while the peak centered at 240 °C was enhanced. This shifting to higher temperature of the dominant peak induces important changes in the dosimetric properties of nanocrystals. The dosimetric behavior for TL method and the TL fading of the samples under β-irradiation was systematically characterized as function of the dopant concentration. The high efficiency of the TL suggest a good potential of this nanophosphor as β- irradiation dosimeter.

The synthesis of europium doped tin oxide, indium oxide and indium tin oxide (ITO) is described. The structure and morphology of mentioned above powders were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The layers with nanocrystalline powders have been fabricated using spin-coating method. The optical and electrical properties of obtained layers have been characterized. The influence of composition on electrical and optical properties was discussed.