Optical properties and electrical bistability of CdS nanoparticles synthesized in dodecanethiol

We reported the synthesis of CdS semiconductor nanoparticles using a simple one-pot reaction by thermolysis of cadmium acetylacetonate in dodecanethiol. Optical measurements of the as-obtained CdS nanoparticles revealed that their optical properties were closely related to surface effects. Based upon the cocktail of poly (N-vinylcarbazole) (PVK) and CdS nanoparticles, a bistable device was fabricated by a simple solution processing technique. Such a device exhibited a remarkable electrical bistability, which was attributed to the electric field-assisted charge transfer between PVK and the CdS nanoparticles capped by dodecaethiol. The conduction mechanism changed from an injection-controlled current to a bulk-controlled one during switching from OFF-state to ON-state.

Optical levitation measurements with intensity-modulated light beams

Illumination of an optically levitated particle with an intensity-modulated transverse beam induces a transverse vibration of a particle in an optical trap. Based on this, the trapping force of a trap can be measured. Using an intensity-modulated longitudinal levitating beam causes a particle to move vertically, allowing for the determination of some aerodynamic parameters of a particle in air. The principles and the experimental phenomena are described and the initial results are given. (C) 1997 Optical Society of America.

Room-temperature spin-oriented photocurrent under near-infrared irradiation and comparison of optical means with Shubnikov de-Haas measurements in AlXGa1-XN/GaN heterostructures

The admixture of linear and circular photogalvanic effects and (CPGEs) in AlxGa1-xN/GaN heterostructures has been investigated quantitatively by near-infrared irradiation at room temperature. The spin-based photocurrent that the authors have observed solidly indicates the sizable spin-orbital interaction of the two-dimensional electron gas in the heterostructures. Further analysis shows consistency between studies by optical and magnetic (Shubnikov de-Haas) measurements on the spin-orbital coupling effects among different AlxGa1-xN/GaN heterostructures, indicating that the CPGE measurement is a good way to investigate the spin splitting and the spin polarization in semiconductors. (C) 2007 American Institute of Physics.

Light-induced evaporative cooling in a magneto-optical trap

This paper presents an experimental demonstration of light-induced evaporative cooling in a magneto-optical trap. An additional laser is used to interact with atoms at the edge of the atomic cloud in the trap. These atoms get an additional force and evaporated away from the trap by both the magnetic field and laser fields. There remaining atoms have lower kinetic energy and thus are cooled. It reports the measurements on the temperature and atomic number after the evaporative cooling with different parameters including the distance between the laser and the centre of the atomic cloud, the detuning, the intensity. The results show that the light-induced evaporative cooling is a way to generate an ultra-cold atom source.

Detection of Brillouin scattering temperature signal in Brillouin optical time-domain reflectometer sensing system based on instantaneous frequency measurement technology

We present a simple and practical method for the single-ended distributed fiber temperature measurements using microwave (11-GHz) coherent detection and the instantaneous frequency measurement (IFM) technique to detect spontaneous Brillouin backscattered signal in which a specially designed rf bandpass filter at 11 GHz is used as a frequency discriminator to transform frequency shift to intensity fluctuation. A Brillouin temperature signal can be obtained at 11 GHz over a sensing length of 10 km. The power sensitivity dependence on temperature induced by frequency shift is measured as 2.66%/K. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Detection of Brillouin scattering temperature signal in Brillouin optical time-domain reflectometer sensing system based on instantaneous frequency measurement technology

abstract {We present a simple and practical method for the single-ended distributed fiber temperature measurements using microwave (11-GHz) coherent detection and the instantaneous frequency measurement (IFM) technique to detect spontaneous Brillouin backscattered signal in which a specially designed rf bandpass filter at 11 GHz is used as a frequency discriminator to transform frequency shift to intensity fluctuation. A Brillouin temperature signal can be obtained at 11 GHz over a sensing length of 10 km. The power sensitivity dependence on temperature induced by frequency shift is measured as 2.66%/K. © 2007 Society of Photo-Optical Instrumentation Engineers.}

Optical transitions of Er3+ and Yb3+ ions in novel oxyfluoride bismuth-germanium glass: Observation of up-conversion

Er3+/Yb3+-codoped novel oxyfluoride bismuth-germanium glass was prepared and its up-conversion fluorescence property under 975 nm excitation has been studied. Intense green and weak red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2), and F-4(9/2) -> I-4(15/2), respectively, were observed at room temperature. The possible up-conversion mechanism was also evaluated. The optimal Yb3+-Er3+ concentration ratio is found based on the direct lifetime measurements of excited levels for Er3+ ion. The structure of this novel oxyfluoride bismuth-germanium glass has been investigated by peak-deconvolution of FT-Raman spectrum, and the structural information was obtained from the peak wavenumbers. This novel oxyfluoride bismuth-germanium glass with relatively lower maximum phonon energy (similar to 731 cm(-1)) can be used as potential host material for up-conversion lasers. (c) 2005 Elsevier B.V. All rights reserved.

Crystal growth and optical properties of Gd1.99-xYxCe.0.01SiO5 single crystals

Gd1.99-xYxCe0.01SiO5 (Ce:GYSO) crystals (x = 0, 0.0995, 0.199) have been grown by the Czochralski (Cz) method. Crystal structure and the distribution coefficients of Ce have been determined for all three crystals. Spectroscopic measurements indicate that optical transmittance and luminescence intensity of Gd1.99-xYxCe0.01SiO5 (x = 0.0995, 0.199) crystals are Substantially higher than those of Ce:Gd2SiO5 (Ce:GSO), especially at x = 0.0995, which makes them good candidate materials for scintillation applications. The particularly important result is that the alloyed Ce:GYSO crystals can be grown easily by the Cz method and, unlike Ce:GSO, they do not undergo cleavage during the growth process or subsequent mechanical treatment. (c) 2005 Elsevier B.V. All rights reserved.

Influences of Al doping concentration on structural, electrical and optical properties of Zn0.95Ni0.05O powders

Nanocrystalline Zn0.95 - xNi0.05AlxO (x = 0.01, 0.02, 0.05 and 0.10) diluted magnetic semiconductors have been synthesized by an auto-combustion method. X-ray diffraction measurements indicate that all Al-doped Zn0.95Ni0.05O samples have the pure wurtzite structure. Transmission electron microscope analyses show that the as-synthesized powders are of the size 40 - 45 nm. High-resolution transmission electron microscope, energy dispersive spectrometer and X-ray photoemission spectroscope analyses indicate that Ni2+ and Al3+ uniformly substitute Zn2+ in the wurtzite structure without forming any secondary phases. The Al doping concentration dependences of cell parameters (a and c), resistance and the ratio of green emission to UV emission have the similar trends. (c) 2007 Elsevier B.V. All rights reserved.

Influence of buffer layer thickness on the structure and optical properties of ZnO thin films

A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12 nm. (c) 2005 Elsevier B.V. All rights reserved.

Measurements of light scattering from glass substrates by total integrated scattering

A total integrated scattering (TIS) measurement was performed to investigate the surface and volume scattering of K9 glass substrates with low reflectance. Ag layers with thicknesses of 60 nm were deposited on the front and back surfaces of the K9 glass substrates by the magnetron sputtering technique. Surface scattering of the K9 glass substrate was obtained by the TIS measurement of the Ag layers on the assumption that the Ag layers and the K9 substrate had the same surface profile. Volume scattering of the substrates was deduced by subtracting the front and back surface scattering from the total scattering of the substrates. (c) 2005 Optical Society of America.

Influence of different post-treatments on the structure and optical properties of zinc oxide thin films

Zinc oxide (ZnO) films with c-oriented were grown on fused quartz glass substrates at room temperature using dc reactive magnetron sputtering. The as-grown films were annealed at 700 degrees C in air and bombarded by ion beam, respectively. The effects of post-treatments on the structural and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. The XRD spectra indicate that the crystal quality of ZnO films has been improved by both the post-treatments. Compared with the as-grown sample, both annealed and bombarded samples exhibited blueshift in the UV emission peaks, and a strong green emission was found in the annealed ZnO film. In both optical transmittance and absorption spectra, a blueshift of the band-gap edge was observed in the bombarded film, while a redshift was observed in the annealed film. (c) 2004 Elsevier B.V. All rights reserved.

Thickness dependence of structure and optical properties of silver films deposited by magnetron sputtering

A series of silver films with different thickness were prepared under identical conditions by direct current magnetron sputtering. The optical properties of the silver films were measured using spectrophotometric techniques and the optical constants were calculated from reflection and transmission measurements made at near normal incidence. The results show that the optical properties and constants are affected by films' thickness. Below the critical thickness of 17 nm at which Ag film forms a continuous film, the optical properties and constants vary significantly as the thickness of films increases and then tends to a stable value which is reached at 41 nm. X-ray diffraction measurements were carried out to examine the structure and stress evolution of the Ag films as a function of films' thickness. It was found that the interplanar distance of (111) orientation decreases when the film thickness increases and tends to be close to that of bulk material. The compressive strains also decrease with increasing thickness. (C) 2007 Published by Elsevier B.V.