Control of spontaneous emission in a five-level system

We study the control of spontaneous emission in a five-level atomic system driven by four fields. We show that with the variation of dynamical variables, namely, Rabi frequencies and carrier phases of driven fields, a wide variety of the spectral behavior can be obtained, including extreme spectral narrowing. Our system can be found easily in real atoms.     

The effect of electric field strength on electroplex emission at the interface of NPB/PBD organic light-emitting diodes

Organic light-emitting diode (OLED) based on two kinds of blue emission materials N,N′-bis(1-naphthyl)-N,N′-diphenyl-l,l′-diphenyl-4,4′-diamine (NPB) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) was fabricated. There is only one emission peak in photoluminescence (PL) spectrum which originates from NPB exciton emission. And the electroluminescence (EL) emission peaks have an apparent red-shift with the increase of driving voltage. The red-shift emission from exciplex emission could be ruled out. Thus, by the method of Gaussian fitting it should be ascribed to the overlap of exciton emission and electroplex emission which occurs at the interface between NPB and PBD. The formation of the electroplex emission under high electric field is analyzed.     

Field electron emission images of multi-walled carbon nanotubes

Field electron emission microscope images from multi-walled carbon nanotubes can typically be characterized by the presence of five pentagons surrounding a sixth central pentagon. The observations of bright line centered interference patterns between adjacent pentagons in the field electron emission microscope images of multi-walled carbon nanotubes have been reported in the literature. We have observed a shift from bright to dark line centered interference patterns and associated this with the presence of surface adsorption. In order to identify the origin of the contaminant, multi-walled carbon nanotubes were dosed with H₂, H₂O, CO and O₂ and then imaged in the field electron emission microscope. Only the samples exposed to O₂ showed a shift from a bright line centered pattern between adjacent pentagons of a clean surface to a dark line centered pattern when one pentagon was contaminated or a bright line centered pattern when both adjacent pentagons become contaminated. The results of the experimental studies and the modeling of the changes in the field emission pattern as phase shifts in the wave function of the tunneling electrons due to modifications in the surface work function are presented.     

Experimental and theoretical studies of electronic energy states of methyl benzoate derivatives

Spectroscopic steady state studies of four monosubstituted derivatives of methyl benzoate dissolved in methylcyclohexane (McH), tetrahydrofuran (THF), ethanol (EtOH) and isopentane-diethyl ether mixture (IP-DE) have been performed at 293 and 77 K. The determined electronic energy values and oscillator strengths are compared with those obtained from quantum chemical calculations. Good agreement between experimental and theoretical energy values is noted. The average value is smaller than 5 percent. A reasonable agreement is noted between intensities of separated bands and oscillator strength of corresponding transitions. The relative ratio of fluorescence to phosphorescence intensity I_fl/I_ph of ortho-substituted compounds dissolved in non-polar, polar and protic solvents is higher than that of the para-substituted derivatives of methyl benzoate. The spectroscopic studies show that methyl ortho-hydroxy benzoate in the excited state S₁ forms H-bonded dimers in the solvents used. At 77 K the dimer fluorescence dominates the phosphorescence emission. The long wavelength absorption band (C) of amino-substituted methyl benzoates consists of two transitions in agreement with our theoretical calculations and a suggestion made by Shabestary and El-Bayoumi [N. Shabestary, M.A. El-Bayoumi, Chem. Phys. Lett. 106 (1984) 107].     

The transient suppression for piezoelectric ceramic emission transducer

A transient suppression method for piezoelectric ceramic transducer is presented. By adding some special pedestal pulses to the original transmitted signal, the transient effects in the output of the transducer can be just precisely transmission by use of a narrowband transducer. canceled, thereby achieving the broadband The experimental results show that the transient responses of the sinusoid pulses and coded signals are suppressed successfully and the acoustic waveforms radiated into the surrounding water are improved significantly.     

Ab initio study of the Ar–CS2(V1B2) intermolecular potential surface: effect of van der Waals interaction on the emission of CS2 molecule

In this work, the excited state intermolecular potential energy surface of the Ar–CS₂(V¹B₂) van der Waals complex was evaluated for the first time. The calculation of more than 4000 single-point interaction energies for the complex using an equation-of-motion coupled-cluster model with single and double substitutions level of theory with extended basis set involving bond functions has been performed. After fitting the interaction energies to analytical functions, the emission spectra of the Ar–CS₂(V¹B₂) complex related to the different stationary points on the potential energy surface were calculated. It was seen that the intensity and the position of the emission spectra are dependent on the orientation of the Ar atom around the bent excited CS₂ and the distance between two components. The information about the structural parameters of the complex related to the global minimum was obtained under the pseudodiatomic approximation with assistance of ab initio potential. The presented investigation could be useful for further theoretical and experimental studies of Ar–CS₂(V¹B₂) complex.     

Effect of Opacity on the Solar Spectral Line of C I 165.7 nm by Escape Factor Treatment

In this article, we report that by using the intensity ratio of the (2-2) to (1-2) component of CI emission lines at about 165.7 nm, we determined the optical depth at the line center of the (2-2) component of CI emission lines by escape factor treatment. The optical depth at the line center of the (2-2) component is calculated to be 0.9998, which is a more reasonable value of solar spectral lines than the value that has been reported. The variation of the optical depth at the line center for different positions from the solar limb is discussed. Using the measured abundance of carbon and the results of ionization balance calculations, we estimate the electron density in the CI emitting region. The density of hydrogen is estimated in the CI emitting region by this method, and is testified to be a better value than the value that has been reported. This discussion will be significant in the analysis of opacity on the solar ultraviolet (UV) or extreme-ultraviolet (EUV) spectrum.     

Empirical,Semi-Empirical and Experimental Determination of K X-Ray Fluorescence Parameters of Some Elements in the Atomic Range 21 ≤ Z ≤ 30

In this study, the semi-empirical and empirical calculations of K X-ray intensity ratios, K-shell fluorescence yields, and vacancy transfer probabilities have been performed for 3d transition elements. Also, σ_Kα, σ_Kβ production cross-sections, K_β/K_α intensity ratios, ω_K fluorescence yields, and η_KL vacancy transfer probabilities of 3d transition elements have been measured. The samples were excited by 59.5 keV γ-rays from a ²⁴¹Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV.     

Light Emission and Scanning Electron Microscopic Characterization of Porous Silicon

Optical emission resulting from sputtered species during ion bombardment of porous and oxidized porous silicon targets has been studied. Samples were bombarded with 5‐keV Kr⁺ ions at an incidence angle of 70 degrees, and the light emitted was analyzed over the wavelength range 200–300 nm. The surface morphology was investigated, and the micrographs revealed grooves parallel to the plane of incidence when the porosity was surprisingly observed in the grooves under each pore. The results are discussed as a function of the incidence angle and the porosity of the silicon targets.