Optical emission from metal targets bombarded by 5–20 keV argon ions

The spectral composition of optical emission from high-purity iron (99.99% Fe), zirconium (99.98% Zr), and tungsten (99.96% W) targets bombarded by 5–20 keV Ar⁺ ions has been studied. The ion-bombardment-induced emission spectra of all metals exhibit two broad bands in the visible and IR spectral range. The first band is assigned to the emission from thermal spikes representing nanosized regions heated to 5000–6000 K, which are formed at the target surface in the course of evolution of high-density atomic collision cascades. The presence of an IR emission band is explained by the integral heating of targets to 500–800 K in the course of ion irradiation. This interpretation is confirmed by agreement between the experimentally measured and calculated temperatures in the region of thermalized collision cascades and the relative intensities of emission bands.     

Spectral Emissivity of Surface Blackbody Calibrators

The normal spectral emissivity of commercial infrared calibrators is compared with measurements of anodized aluminum samples and grooved aluminum surfaces coated with Pyromark. Measurements performed by FTIR spectroscopy in the wavelength interval from 2 to 20 μm and at temperatures between 5 and 550°C are presented with absolute uncertainties from 0.25% to 1% in spectral regions with sufficient signal and no significant atmospheric gas absorption. A large variation in emissivity with wavelength is observed for some surfaces, i.e., from 1% to 3% to more than 10%. The variation in emissivity using similar materials can be reduced to 0.5–1% by optimizing the coating process and the surface geometry. Results are discussed and an equation for calculation of the equivalent blackbody surface temperature from FTIR spectra is presented, including reflected ambient radiation. It is in most cases necessary to correct temperature calibration results for calibrators calibrated at 8–14 μm to obtain absolute accuracies of 0.1–1°C in other spectral regions depending on the temperature. Uncertainties are discussed and equations are given for the correction of measured radiation temperatures.     

Optical and dielectric properties of lanthanide titanium tantalate and niobate ceramic composites

The xPrTiTaO₆ (1 − x) YTiNbO₆ dielectric ceramic composites are fabricated through the solid state ceramic route. The compositions are calcined in the temperature range 1,200–1,260 °C and sintered in the range 1,350–1,410 °C. Structural analysis of the materials is done using X-ray Diffraction analysis. The composites contain both aeschynite and euxenite orthorhombic phases. The surface morphology of the sintered pellets is examined by scanning electron microscopy. The dielectric constant, conductance and loss factor are measured in the radio frequency region. The UV–visible spectra are recorded and the band gap is calculated. The photoluminescence spectra of the compositions are recorded and the transitions causing emission are identified. The elemental composition of the composites is confirmed using energy dispersive spectroscopy. The materials are suitable for substrate and optoelectronic applications.     

Determining local temperatures in the structures of AlInGaP/GaAs red LEDs in a pulsed operation regime

The emission spectra of AlInGaP/GaAs red light-emitting diodes (LEDs) based on a multi-quantum-well heterostructure with distributed Bragg reflectors, operating in a pulsed mode with a pulse repetition rate within 1–10 kHz and a current of 1 × 10⁻³−2 × 10⁻¹ A have been studied in the 20–100°C temperature range. In the regimes with short current pulses and large off/duty ratios, which exclude self-heating of the LED structure, the temperature dependences of the wavelength of emission peaks in the main and side bands exhibit a super-and sublinear behavior, respectively. In the quasi-linear regions of these dependences, the temperature coefficient of wavelength shift for the main peak decreases, while that for the side peak weakly increases with increasing current. The local temperatures (determined from the spectral shift of the main and side emission peaks) and their difference increase with the pulse duration. The difference of thermal resistances, which is calculated from the slope of a plot of the local temperature versus average heating power, is independent of the current and determined by the parameters of layers separating the heterostructure from the reemission region.     

Calculation of the integral optical characteristics of a sodium plasma

The emissivities of a plane layer and a hemispherical volume and also the Planck and Rosseland mean values of a sodium plasma are calculated in the range of temperatures 1000–20,000 K and pressures 0.1–20 bar. In determination of the spectral coefficient of absorption the entire spectral interval in which the main part of radiant energy is transferred is taken into account, and also the most important radiation processes that are associated with free-free, bound-free, and bound-bound transitions are considered. For the first time, the effect of internal microfields in the plasma is taken into account, thus allowing a correct calculation of the populations of excited states, shift of ionization equilibrium, and a smooth transition of the line spectrum into a continuous one in the near-threshold regions. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 5, pp. 945–952, September–October, 2000.     

The influence of longitudinal magnetic field on recombination radiation of low-pressure glow discharge in hydrogen and helium

We study the influence of longitudinal magnetic field on the radiation of low-pressure glow discharges in hydrogen and helium. We conducted experiments under a pressure in a discharge chamber of 10–20 Pa and a discharge current of 10–20 mA. A 0–1600 G magnetic field influenced only the cathode parts of the discharge, negative glow, and the dark Faraday space. The electron temperature and density were measured by the two-probe method as a function of magnetic field. We studied the dependence of the intensity of radiation in the spectral lines and continuous spectrum on magnetic field induction. We discovered that, under the action of magnetic field, discharge in hydrogen and helium is compressed and its glow volume increases by a factor of 20–25. In contrast, the radiation intensity in the lines and continuous spectrum increase by a factor of 100–200. We found a strong discrepancy in the measured intensity of the continuous spectrum into spectral ranges with calculation of electron-ion recombination.     

Pulsed cathodoluminescence of calcite crystals of various origins

We have studied the luminescence of calcites from phlogopite-calcite veins, marbles, leucogranites, apatite-calcite ores, and carbonatites in the spectral range 300–800 nm under excitation with nanosecond electron pulses at an electron beam current density of ∼10 A/cm². All of the calcite varieties have a fast emission component, with a broad spectrum in the near-UV and visible spectral regions, whose decay time is comparable to the excitation pulse duration, and a slow emission component, with a peak-emission wavelength of 610–620 nm and decay time of tens of milliseconds. The spectral composition of the emission depends on the nature of the calcite sample. We analyze the evolution of the spectrum after excitation and discuss the luminescence excitation mechanisms and the nature of the emission centers.     

Visible photoluminescence of hydrothermal synthesized Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanostructures

Sn_1−x Ni _x O₂ nanostructures such as nanocubes, nanospheres and hollow spheres were synthesized by a simple hydrothermal method. Room temperature photoluminescence spectra of the as-synthesized samples display a strong yellow emission at about 600 nm and a weak blue emission at about 430 nm. The as-prepared and annealed Sn_1−x Ni _x O₂ (x = 0, 0.01, 0.02, 0.04) were characterized by X-ray diffraction, field emission scanning electron microscopy, Raman spectrum, UV–Vis absorption spectra, and room temperature photoluminescence spectra. By investigating the relationship between the Raman band centered at 560 cm⁻¹ and the photoluminescence of the samples, we suggest that the broad yellow emission and weak blue emission primarily originate from singly ionized oxygen vacancies and tin interstitials, respectively.     

Armco Iron Normal Spectral Emissivity Measurements

Directional spectral emissivity data in different environments are needed in a great number of scientific and technological applications. In this work, the normal spectral emissivity of Armco iron is studied as a function of temperature under a controlled atmosphere. Emissivity values are calculated by the direct radiometric method. The evolution with thermal cycling, the dependence on temperature, and the effect of surface roughness are considered. Additionally, the electrical resistivity is calculated by using the Hagen–Rubens emissivity relation. This work makes progress in the use of Armco iron as an emissivity reference.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Reconstruction of the X-ray emission spectrum of a nanosecond creeping discharge

A method is proposed for determining the soft x-ray emission spectrum of a nanosecond creeping discharge. The method includes a determination of the photoelectron density from photocurrent measurements and a calculation of the spectral flux density. The results are compared with experimental data on the wavelength interval of maximum radiation intensity. Pis’ma Zh. Tekh. Fiz. 24, 39–44 (April 12, 1998)     

Photoluminescence of copper ion exchange BK7 glass planar waveguides

Copper–alkali ion exchange technology was used to prepare BK7 glass planar waveguides. The photoluminescence spectra of the waveguides were studied with fluorescence spectrophotometer. It was observed that there were strong emission peaks at around 520 nm, which were strongly influenced by the ion-exchange times. Besides the time, the ion-exchange temperature was important factor as well, the higher ion-exchange temperature was found to bring a blue shift of emission spectra. The blue–green emission band originates from different transition mechanism of energy level. The spectroscopy features of copper within the glass host were also affected by the excitation wavelength, which resulted in a shift of the emission band peaks.     

Effect of the odd intensity parameters and optical properties of Tb3+ doped fluoroindate glasses

In the present paper we report on the detailed spectroscopic analysis of the Tb³⁺-doped fluoroindate glasses with different Tb³⁺ concentration. Absorption spectra in the spectral range from 320 to 6,000 nm were recorded and analyzed for all samples by applying the standard and modified Judd–Ofelt theory. It is well known that in some cases application of the standard Judd–Ofelt theory results in getting negative values for the Ω₂ intensity parameter, which is in obvious contradiction to the definition of the Ω_λ (λ = 2, 4, 6) parameters. We demonstrate that it is possible to obtain positive values for all intensity parameters Ω_λ by including the odd intensity parameters (λ = 1, 3, 5). Using the standard and modified Judd–Ofelt theory, we obtained the values of the intensity parameters and calculated the oscillator strengths and branching ratios for electric dipole optical transitions in all samples. Comparison with experimental data is discussed.     

Fatigue life under variable-amplitude loading according to the cycle-counting and spectral methods

We compare the values for the fatigue life of 12010.3 steel determined experimentally under variable-amplitude tension-compression and calculated by two methods in time and frequency ranges. The first method is based on the schematization of the loading history and uses the rainflow algorithm. The fatigue life was calculated according to the Serensen-Kogaev linear hypothesis of damage accumulation wit the use of the Manson-Coffin dependence. The second method is based on power spectral density functions. These methods differ in the approaches used for the determination of the probability density of amplitude distribution from the deformation history. It is established that, in the case considered, the values of fatigue life calculated by the cycle-counting method and by the spectral method are close to the values determined experimentally. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 121–128, May–June, 2006.     

Photoluminescent properties of ZnS:Mn nanoparticles with in-built surfactant

Mn-doped ZnS nanoparticles, having average diameter 3–5 nm, have been synthesized using chemical precipitation technique without using any external capping agent. Zinc blende crystal structure has been confirmed using the X-ray diffraction studies. The effect of various concentrations of Mn doping on the photoluminescent properties of ZnS nanoparticles has been studied. The time-resolved photoluminescence spectra of the ZnS:Mn quantum dots have been recorded and various parameters like lifetimes, trap depths, and decay constant have been calculated from the decay curves at room temperature. The band gap was calculated using UV–Visible absorption spectra.     

Temperature dependent growth and optical properties of SnO<Subscript>2</Subscript> nanowires and nanobelts

SnO₂ nanowires and nanobelts have been grown by the thermal evaporation of Sn powders. The growth of nanowires and nanobelts has been investigated at different temperatures (750–1000°C). The field emission scanning electron microscopic and transmission electron microscopic studies revealed the growth of nanowires and nano-belts at different growth temperatures. The growth mechanisms of the formation of the nanostructures have also been discussed. X-ray diffraction patterns showed that the nanowires and nanobelts are highly crystalline with tetragonal rutile phase. UV-visible absorption spectrum showed the bulk bandgap value (∼ 3–6 eV) of SnO₂. Photoluminescence spectra demonstrated a Stokes-shifted emission in the wavelength range 558–588 nm. The Raman and Fourier transform infrared spectra revealed the formation of stoichiometric SnO₂ at different growth temperatures.     

The estimation of the power spectrum of a signal

An algorithm is considered which enables the power spectrum to be estimated for a discrete sample of N values of the signal in a time interval of [−T/2, +T/2] using a filter which has the narrow spectral band as a rectangular time window, but with a sidelobe level of less than 4.3 dB. Examples of several “power” filters are presented. Translated from Izmeritel'naya No. 9, pp. 65–66, September, 2008.     

Luminescence analysis of Eu complexes containing diphenanthryl β-diketone ligands doped silicone rubber

Two Eu complexes containing symmetrical and asymmetrical diphenanthryl β-diketone ligands have been incorporated into silicone rubber. Their luminescence properties have been investigated by luminescence spectra and lifetime measurements. According to the fluorescence emission spectrum, the Judd–Ofelt parameters Ω₂, Ω₄ of europium complexes doped silicone rubber have been calculated and the influence of ligand’s symmetry on the luminescence properties of Eu complex doped silicone rubber was discussed.     

Coupled Phonon-Ripplon Modes in the Electron Crystal at Different Driving Fields

Coupled phonon-ripplon oscillations in a two-dimensional electron crystal over liquid helium with surface electron density n _s =1.2×10⁹ cm⁻² at the temperature T=83 mK are studied in a Corbino experimental cell. The measurements are performed in the frequency interval where resonances of the coupled oscillations are observed and at different driving voltages V _∥ <10 mV at which nonlinear features in the crystal conductivity start to appear. A special attention is paid to a relatively narrow frequency interval ω/2π≃3–5 MHz. In this interval the jumps in the oscillation spectrum are observed. From the data obtained, the mobility and electron effective mass are calculated as functions of driving electric field. The electron effective mass in the crystal and dissipative losses are found to increase with the driving field increase. A possible reason for that can be an anharmonicity of the electron-ripplon interaction, which become noticeable if the electron crystal velocity along the surface is high enough.     

Bremsstrahlung radiation from high-energy electrons in wide gas-filled gaps

Electric discharge in wide interelectrode gaps filled with air at atmospheric pressure have been experimentally studied using applied voltage pulses with amplitudes up to 800 kV and a front width within 150–200 ns. The discharge was accompanied by the emission of a 10–20-ns-long pulse of radiation with photon energies above 5 keV. It is established that this emission is related to the generation of runaway electrons from the heads of anode-directed streamers. The calculated spectrum of the observed bremsstrahlung radiation exhibits a maximum at photon energies about 15 kV, which is due to the absorption of photons by the molecules of a gas in which the discharge takes place.