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Infrared-to-visible upconversion (IVU) possesses a variety of applications, spanning from bio-imaging to anti-counterfeiting, and has attracted great attention. However, the devices developed in previous studies suffer from several drawbacks, such as relatively weak optical absorption, requirement of a complicated design, and a costly fabrication process, which limit their potential practical application. To circumvent the existing difficulties, in this study, an IVU device based on infrared quantum dots (QDs) and a mixture of visible QD light-emitting diodes (QLEDs) with low operational voltage and multiple changeable visible colors is demonstrated. The emission color of this IVU-QLED can be easily manipulated under different input currents and power densities of incident infrared radiation. The IVU-QLED device can also be achieved with cost-effective and simple solution fabrication processes. In addition, this dual electrical-optical modulated IVU-QLED shows a fast response time. With the unexplored features of IVU, including infrared-visible upconversion, tunable visible color emission, dual functional modulation, and cost-effectiveness, the designed IVU-QLEDs shown here provide an alternative route for the development of untouched optoelectronic devices, which should be very useful and timely for future applications covering anti-counterfeiting, infrared sensing, bio-imaging, night vision, etc. [ABSTRACT FROM AUTHOR]

Converting ambient thermal energy into electricity is of great interest in harvesting energy from the environment. Piezoelectric cantilevers have previously been shown to be an effective biosensor and a tool for elasticity mapping. Here we show that a single piezoelectric (lead-zirconate titanate (PZT)) layer cantilever can be used to convert heat to electricity through pyroelectric effect. Furthermore, piezoelectric-metal (PZT-Ti) bi-layer cantilever showed an enhanced induced voltage over the single PZT layer alone due to the additional piezoelectric effect. This type of device can be a way for converting heat energy into electricity. [ABSTRACT FROM AUTHOR]

The ultraviolet (UV) electroluminescence (EL) from the TiO2/ZnO coaxial nanowires (NWs)/poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate) inorganic/organic heterostructure devices is greatly enhanced and the defect emission is significantly suppressed compared with the uncoated ZnO NW device at room temperature. The origins of the great changes in EL of ZnO NW devices are attributed to the surface modification of the sputtered TiO2 coating and the reduction in the pinhole traps on the surface of ZnO NWs. It is found that for the optimized device, the EL intensity ratio between the band gap and defect emission can be greatly enhanced by up to about 250 times its prior level. Such ZnO NW devices with enhanced UV emission have potential applications in the highly efficient solid state emitters. [ABSTRACT FROM AUTHOR]

A thermal emitter with selective wavelength has been demonstrated in which the dielectric layers formed one-dimensional photonic crystals are sandwiched between two Ag films. The top Ag film is perforated periodically with hexagonal hole array. The selected thermal radiation of the photonic crystals resonates between two metal films and surface plasmon polaritons are generated on the top Ag and converted to light radiation. It is found that when leakage modes adjacent to the optic band gap of photonic crystals meet the resonant modes of surface plasmom polaritons, an enhanced thermal emission with maximum intensity can be obtained. The hybrid photonic and plasmonic thermal emitters are selective, which should be very useful for the creation of high power infrared light sources. [ABSTRACT FROM AUTHOR]

It is demonstrated that magnetic periodic arrays can be easily fabricated from direct writing water developable La0.7Sr0.3MnO3 electron beam resist. Two unique features of our approach are (1) the patterned La0.7Sr0.3MnO3 resist film can be developed using nontoxic and environmentally friendly pure water and (2) either positive or negative patterns can be fabricated depending on the dosage of electron beam. The mechanism of the dual function characteristic of the resist was studied using Kelvin probe microscope. The surface potential of patterned La0.7Sr0.3MnO3 resist increases with increasing electron beam dosage due to the changes of resist composition. The formations of periodic magnetic arrays were confirmed by the studies of scanning electron microscope and magnetic force microscope. The magnetization of La0.7Sr0.3MnO3 can be enhanced by postsintering the sample at 900 °C after electron beam irradiation. We have therefore provided a one-step, simple, and convenient alternative technique for the fabrication of nanoscale magnetic patterns, which form the building blocks for the study of physical properties in periodic magnetic arrays. [ABSTRACT FROM AUTHOR]

An organic two-terminal phototransistor structure for information technology has been designed, fabricated, and demonstrated. The device comprises a resistive random access memory (RRAM) in tandem with an organic solar cell (OSC). The transistor effect is realized by the functional integration of both individual devices; i.e., the photocurrent produced by the OSC is manipulated through the switchable RRAM. Compared with conventional phototransistors, our design possesses several intriguing features, including ultra-fast photoresponse time, controllable photocurrent, and solution processable active layers. Most importantly, these operational properties are achievable with only two vertically sandwiched electrodes, which are beneficial for high speed optical communication, circuit miniaturization, and energy saving. These unique features make it a good candidate for implementation in optical communication with diverse applications such as Li-Fi technology and security encryption. [ABSTRACT FROM AUTHOR]

Discusses a study on the observation of the quantum confinement effect by using photothermal deflection spectroscopy and photoluminescence experiments of cadmium sulphide and cadmium selenide quantum dots. Analysis of quantum confinement effect; Measurement of absorption spectra; Source of ionization of microcrystals.

Presents a study which evaluated the morphologies and photoluminescence of porous silicon under different etching and oxidation conditions. Details on the experiment; Results of the study; Discussion of findings.

Presents a study that investigated the material properties of In[subx]Ga[sub1-x]As epilayers on gallium arsenide by molecular-beam epitaxy. Interpretation of the cross-sectional transmission electron microscopy images for the heterojunctions; Relation used to estimate the upper limit of threading dislocation density in terms of the full width at half-maximum of the (400) double-crystal x-ray diffraction signal; Analysis of the magnetophotoconductivity signals.

Reports on the photoconduction of synthetic pyrite FeS[sub2] single crystals with low impurity concentration prepared by chemical vapor transport. Experimental details; Results and discussions.

Based on the concept of optical enhancement in nanoparticle-mediated coupling, a novel composite consisting of ZnO nanorods and ZnO nanoparticles has been synthesized and characterized. The ZnO nanoparticles can be regarded as light-coupling media to increase the absorption cross section of excitation light as well as the emission extraction efficiency due to the relaxation of momentum selection rule. With our devised ZnO nanostructures, the band gap emission of ZnO nanorods can be enhanced by up to 8.5 times. The strategy of optical enhancement provided here should be very useful in designing many other nanostructures for high efficiency optoelectronic devices. [ABSTRACT FROM AUTHOR]

The femtosecond pulsed Z-scan measurements of the resonant nonlinear optical absorption of the InN epitaxial films in the range of 720–790 nm were reported. The absorption saturation behavior was found to gradually decrease with increasing photon energy. The nonlinear optical absorption cross sections of the InN films were estimated and the values are found to be in good agreement with the calculations based on the band-filling model. These results are relevant for the future development of nonlinear optical devices based on InN. [ABSTRACT FROM AUTHOR]

Presents a study which determined gap state density distribution in hydrogenated amorphous silicon from light-induced effects. Details of the experimental techniques used; Techniques that can be used in determining gap state density; Effect of illumination on the activation energy in hydrogenated amorphous silicon.

We demonstrate a facile annealing method to improve the polymer chain ordering of poly(3-hexythiophene) (P3HT):fullerene blend triggered by a small amount of FePt nanowires (FePt NWs). By applying a magnetic field perpendicular to the substrate during the solvent drying process, the resulting P3HT:fullerene:FePt NWs film becomes highly optical anisotropy and exhibits a much stronger X-ray diffraction intensity of P3HT. We hypothesize that the coupling force between the FePt NWs and P3HT can assist the polymer chain alignment leading to an improved device performance. The proposed approach is simple and can be applied to other polymer blend systems as well. [ABSTRACT FROM AUTHOR]

We have developed a pyroelectric field effect transistor (FET) based on a graphene-lead zirconate titanate (PZT) system. Under the incidence of a laser beam, the drain current can be increased or decreased depending on the direction of the polarization of the PZT substrate. The drain current sensitivity of the optothermal FET can reach up to 360 nA/mW at a drain field of 6.7 kV/m more than 5 orders of magnitude higher than that of the photogating transistors based on carbon nanotube on SiO2/Si substrate. Graphene is an excellent component for pyroelectric FET due to its high optical transparency and conductance. [ABSTRACT FROM AUTHOR]

Deals with a study which investigated the effect of monochromatic light exposure with different photon energies in order to explore the creation process of optically induced excess conductivity in compensated hydrogenated amorphous silicon films. Methods; Results; Discussion.

Room-temperature visible lasing in CdSe semiconductor nanotube arrays embedded in anodic aluminum oxide template has been demonstrated. The cylindrical nanocavities of anodic aluminum oxide template form laser resonators, and the laser oscillation was achieved through whispering gallery mode gain from the interior semiconductor nanotubes. The linearly polarized stimulated emission, the one dimensionality, and the chemical accessibility to nanotubes render them significant potential for serving as various applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

The authors provide direct evidence of non-180° domain switching in the piezoelectric response of substrate-free 40 μm thick polycrystalline [Pb(Mg1/3Nb2/3)O3]0.63(PbTiO3)0.37 (PMN-37PT) sheets under dc electric fields through piezoresponse force microscopy (PFM) at the single grain level. The sheet’s polarization preferred pointing in the planar direction which was switched to the normal direction at electric field ranging between 1.3 and 1.9 kV/cm. An independent d31 measurement of PMN-37PT sheets deduced from the axial tip displacement measurements of a 4 mm long PMN-PT/copper cantilever showed enhanced d31 values that peaked at –2700 pm/V in the same range of electric field, consistent with the PFM observation. [ABSTRACT FROM AUTHOR]

Infrared lasing from single-crystalline InN nanobelts grown by metal organic chemical vapor deposition was demonstrated. Transmission electron microscopy studies revealed that the InN nanobelts of rectangular cross section grew along [110] direction and were enclosed by ±(001) and ±(110) planes. The infrared lasing action was observed at 20 K in the InN nanobelts grown on an amorphous silicon nitride coated silicon substrate by continuous wave laser pumping. [ABSTRACT FROM AUTHOR]

Nonlinear optical properties of ZnO nanorods (NRs) are strongly influenced by its dimension and aspect ratio. Size-dependent second harmonic generation (SHG) in ZnO NRs has been investigated with polarized excitations recently. However, detailed description to the SHG dependency with NR dimensions has not yet been given. In this paper, the relationship between rod diameter/length and corresponding χ(2) values based on Lorentz local field is established, both theoretically and experimentally, for the first time. Theoretically, Lorentz local field induced spectral red shift and the consequent dielectric constant modification is used to elucidate the size effect for χ(2) under the condition that both excitation and SHG wavelengths are far from the band gap. Experimentally, χ(2) of ZnO nanorods with various sizes is measured via Maker fringe technique, and the results fit well to our theory. [ABSTRACT FROM AUTHOR]

It is shown for the first time that hydrogen passivation can be made by using a photochemical vapor deposition system. Unlike the common methods, this new method of hydrogenation has no electron or ion bombardment, thus the sample surface will not be damaged during processing. The effects of hydrogenation are confirmed by the enhancement of photoluminescence intensity. A strong increase in the luminescence intensity (a factor of 23) has been observed which is comparable to the results of rf glow discharge systems. [ABSTRACT FROM AUTHOR]

Light-induced metastable defects in hydrogenated amorphous silicon can be eliminated by atomic hydrogen at the temperature below which the annealing effect occurs. The resulting material has a very high photosensitivity and stability. [ABSTRACT FROM AUTHOR]

We report the influence of carrier reflector and back surface field generated by doped graphene on n-ZnO nanoridges/p-silicon photodetectors and silicon solar cells. It is found that the p-type graphene not only acts as an electron blocking layer, but also helps the collection of photogenerated holes. Quite surprisingly, the on/off ratio of the photodetector with the insertion of doped graphene can be increased by up to 40 times. Moreover, we demonstrate that typical silicon solar cells with the doped graphene, the cell efficiency can be enhanced by about 20%. Our approach would expand numerous applications for graphene-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

The resonant coupling between cadmium-free I-III-VI2 group quantum dots (QDs) and metal nanostructures has been investigated. Via a SiO2-packaging synthetic procedure, the emission intensity of green ZCIS/ZnS QDs can be greatly enhanced by three times through the localized surface plasmon of Au nanoparticles. Moreover, the bandwidth of the emission spectrum can be narrowed by 17 nm, and the resultant quantum yield is more than 50% which sets up the highest reported value up today for green I-III-VI2 QDs. Our strategy for the improved characteristics of emission spectrum may open a facile alternative for the development of cadmium-free QD light emitting diodes and other optoelectronic devices. [ABSTRACT FROM AUTHOR]