The persistent energy transfer of Eu and Mn and the thermoluminescence properties of long-lasting phosphor Sr3MgSi2O8:Eu, Mn, Dy

Eu²⁺, Mn²⁺ and Dy³⁺ co-doped long-lasting phosphors Sr₃MgSi₂O₈ were prepared by a solid-state reaction under a reductive atmosphere. Fluorescence spectra demonstrated that the weak red emission resulting from the forbidden transition of Mn²⁺ could be enhanced by the energy transfer from Eu²⁺ to Mn²⁺. The energy transfer between Eu²⁺ and Mn²⁺ was systematically investigated. The phosphorescence spectra revealed that Eu²⁺ could persistently transfer its energy to Mn²⁺ after removing the excitation source. The duration of Mn²⁺ can prolong to more than 2 h. The thermoluminescence spectra were used to characterize the ability of the trap to trapping the carriers. By the analysis of the ionization potentials, the roles of Mn²⁺ and Dy³⁺ in the afterglow process were discussed. A possible afterglow mechanism was presented and discussed.     

Optical temperature sensing based on the luminescence from YAG:Pr transparent ceramics

The YAG:Pr transparent ceramic was fabricated using a conventional solid-state reactive method to explore its possible application in optical thermometry. Photoluminescence and temperature-dependent luminescence were elaborately investigated under 452 nm excitation. The ceramic showed two intrinsic emission bands at 488 and 594 nm, which were attributed to characteristic Pr³⁺: ³P₀ → ³H₄ and ³P₁ → ³H₆ transitions, respectively. Down-conversion emissions from the two thermally coupled excited states of Pr³⁺ were recorded in the temperature range of 293–593 K. The Boltzmann distribution theory was adopted to interpret the temperature-dependent luminescence of Pr³⁺. The temperature sensitivity exhibited an increasing trend with the increase of temperature, typically, 0.0025 K⁻¹ at 593 K. The results indicated that the present ceramic was a promising candidate for optical temperature sensor.     

Arrhenius and the temperature dependence of non-constant failure rate

This paper examines the temperature dependence of component hazard rate for the cases of log-normal and Weibull failure-time distributions and shows that the common belief that the temperature variation of component failure rate follows the Arrhenius rule can be substantially in error. Although most failures in present-day equipment are not due to defective components, the paper also examines the temperature dependence of equipment rate of occurrence of failure having a power-law or negative exponential variation with time for the temperature range where the majority of failures are due to rate processes obeying the Arrhenius equation. The consequences of a Gaussian distribution of failure-mechanism activation energy in a device population are also considered. Although the temperature dependence of failure rate can be very high, in most situations it is much less than that of the Arrhenius acceleration factor. It is very improbable that the temperature dependence of component failure rate can be meaningfully modelled for reliability prediction purposes or for the purpose of optimizing thermal design component layout. Attention is drawn to the invalidity of determining the failure activation energy from the average failure rates in accelerated high-temperature time-terminated life tests.     

Surface tension of pure liquid bismuth and its temperature dependence: Theoretical calculations

A theoretical method for calculating the surface tension of liquid metals as a function of temperature is proposed. A mathematical equation, based on statistical thermodynamics, is applied to calculate the surface tension of pure liquid bismuth, in the temperature range 545-620 K. The calculated surface tension of liquid bismuth was found to be 388 mJ/m², which is in excellent agreement with the reported experimental values (374-417 mJ/m²). The surface tension of bismuth decreases linearly with temperature, confirming a negative slope.     

Preparation, characterization and luminescence of a new green-emitting phosphor: Gd2TeO6 doped with Tb

Novel green-emitting Gd_2 − xTb_xTeO₆ powder phosphor has been prepared by the oxidation of corresponding rare-earth oxytellurides. The photoluminescence (PL) properties were reported. Five dominant bands centered at 302 nm, 318 nm, 339 nm, 353 nm and 378 nm characterize the excitation spectrum. Under the excitation of 378 nm UV light, the emission spectrum exhibits an intense peak centered at 543-548 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺. This phosphor can be excited by light with wavelengths of 350-400 nm and therefore can be used as a green phosphor for white lighting devices utilizing near-UV LED as a light source.     

The effects of binding type on luminescence LED phosphor based on GGG/Ce3+

Luminescence and reflectance spectra of coatings based on gadolinium gallium garnet doped by cerium (GGG/Ce³⁺) with silicone resin or potassium liquid glass compound were analyzed depending on concentration. It was established that the maximum emissions of the coatings at 75 wt.% compound concentration have luminescence band at 570 nm and absorption band at 470 nm. Both bands were detected by absorption or emission of cerium ions in gadolinium gallium garnet. Ce³⁺ ion transition into Ce⁴⁺ ion was observed upon quantum absorption, and the reverse transition was observed upon quantum emission.     

The UV and VUV luminescence properties of the phosphor Mg2GeO4:Tb

A novel green phosphor Mg₂GeO₄:Tb³⁺ with pure phase was prepared by the solid state reaction. The luminescence properties were investigated in detail. The diffusion reflection spectra of the undoped and Tb³⁺ doped Mg₂GeO₄ phosphors were recorded, the result reveals that there is an absorption band superposition of the host material and Tb³⁺ ion. The study on the excitation and diffusion spectra shows that there is an effective energy transfer from the host material to Tb³⁺ ion. Under 277 and 172 nm excitation, the phosphor presents predominant green emission at 543 and 547 nm respectively. The excitation intensity at 172 nm is about 1.8 times of that at 272 nm. The promising luminescence properties make it a candidate for application in Plasma Display Panel.     

On the temperature dependence of the London penetration depth in a superconductor

In the framework of the electron-phonon theory of superconductivity [1], it is shown that the magnetic field penetration depth _L increases like a certain power of temperature atTT _c due to the low-lying excitations in the phonon spectrum. For the acoustic phonons with the density of states ² the penetration depth increases T ⁵. The origin of such a high power ofT is the same as that in the case of resistivity of the normal metal: the phonon corrections to the electromagnetic vertex should be taken into account, and major terms (T ³) cancel, the surviving ones having a higher power ofT. The possibility of linear and quadratic terms in _L(T) is discussed in a model of electrons interacting with two-level centers [2].     

Energy transfer and luminescence properties of Eu-doped NaTb(WO4)2 phosphor prepared by a facile hydrothermal method

NaTb_(1−x)Eu_x(WO₄)₂ (x = 0-100%) phosphors have been synthesized via a mild hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation and emission spectra and decay curve were used to characterize the samples. Moreover, the luminescence colors of NaTb_(1−x)Eu_x(WO₄)₂ (NTbW:Eu) samples can be tuned from green, green-yellow, and yellow to red by simply adjusting the relative Eu³⁺-doping concentrations under a single wavelength excitation, which might find potential applications in the light displays systems.     

The spectral resolution of high temperature GaAs photon counting soft X-ray photodiodes

Circular mesa GaAs p⁺-i-n⁺ diodes for photon counting soft X-ray spectroscopy have been fabricated and characterised over a temperature range of +80 to -30 °C. The spectroscopic performance of the diodes, as measured by the FWHM of the Mn K_α X-ray line from an ⁵⁵Fe radioisotope, is reported. In addition, we compare the GaAs diodes with previously fabricated and characterised Al_0.8Ga_0.2As p⁺-i-n⁺ diodes of similar geometry.     

Dependence of fading patterns of photo-stimulated luminescence from imaging plates on radiation, energy, and image reader

We have been investigating the fading characteristics of imaging plates (IPs) as integral type detectors. The dependence on alpha, beta, and gamma ray radiation and their energies of the fading effect was measured using three types of IPs (BAS-UR, BAS-TR, and BAS-MS). The functions to correct the fading were determined by using the method reported in a previous paper. In all types of IPs, we confirmed that the fading effect is independent of the energy of the incident particles of beta and gamma rays and also independent of radiation except for the first component, which fades out in a very short time after irradiation with alpha rays. These results are very useful in the utilization of IPs as integral detectors in practical radiation fields.

Empirically, the fading pattern is known to change when the IP is scanned by different types of image readers. The differences in the fading patterns obtained with two types of image readers, the BAS-1000 and the BAS-5000 (Fuji Film Co.), is discussed. Development of an equation for correcting the effects of the differences in the image readers was attempted.     

The design of a piezoelectric resonance sensor of ionizing radiation

It is shown that it is possible to increase the sensitivity of a sensor to characteristic radiation by concentrating the electric-field strength under resonance conditions in metal-oxide-metal structures. __________ Translated from Izmeritel’naya Tekhnika, No. 3, pp. 47–51, March, 2008.     

Simultaneous breakaway of a dislocation from several pinning points

The amplitude-dependent internal friction (ADIF) of very pure aluminum (99.9999%) and Al dilute alloys (20–100 ppm) has been measured at temperatures between 2 and 240 K. Two universal properties have been found in the temperature dependence of the required stress amplitude for a constant decrement. At relatively low temperatures (or high stress amplitude), the decrease of the stress with increasing temperature is proportional to T^2/3 down to 65% of the stress for 0 K, and then deviates from the T^2/3 dependence. It is explained that the elementary process is due to unpinning of a dislocation from a single solute atom. The interaction potential has been determined successfully from this region (above 40% of the stress at 0 K). At relatively high temperatures (or stress less than 40% of that for 0 K), we find for the first time that the stress changes as proportional to T⁻¹ for all dilute Al alloys but for a pure Al crystal. It is explained that the elementary process is due to simultaneous unpinning of a dislocation from several solute atoms for dilute alloys.     

Evaluation of the GSO:Ce scintillator in the X-ray energy range from 40 to 140 kV for possible applications in medical X-ray imaging

The purpose of the present study was to evaluate, under X-ray medical imaging conditions, the X-ray luminescence efficiency (XLE) and the optical quantum gain (OQG) of the Gd₂SiO₅:Ce scintillator in single crystal form, suitable for tomographic applications. Intrinsic physical properties and light emission characteristics of the Gd₂SiO₅:Ce scintillator, were also studied. Both experimental and Monte Carlo techniques were used. Various X-ray tube voltages (40–140 kV), currently employed in X-ray imaging applications, were used. XLE was found to vary slowly with X-ray tube voltage from (0.021±0.003) to (0.017±0.003). OQG varied from (317±18) to (466±23) light photons per incident X-ray. These values were adequately high for imaging applications using the particular energy range. Additionally, it was found by Monte Carlo simulations that for crystal thicknesses higher than 0.5 cm both XLE and OQG reached saturation levels, indicating that higher thickness crystals are of no practical use in X-ray medical imaging.     

The study of graphite disordering using the temperature dependence of ion-induced electron emission

The temperature dependences of ion-induced electron emission yield γ(T) under 6-30 keV N₂⁺, Ne⁺, Ar⁺ and 15 keV N⁺ high-fluence ion irradiation of polycrystalline graphite at normal ion incidence have been analyzed to trace the structure change dependence depending on irradiation temperature and the level of radiation damage v measured in dpa (displacements per atom). It has been found that, under irradiation at room temperature, the threshold value for graphite lattice disordering equals v_d ≈ 60 dpa for noble gas ions (Ar⁺, Ne⁺) and ν_d ≈ 40 dpa for N₂⁺.     

The use of energy windowing to discriminate SNM from NORM in radiation portal monitors

Energy windowing is an algorithmic alarm method that can be applied to plastic scintillator-based radiation portal monitor (RPM) systems to improve operational sensitivity to certain threat sources while reducing the alarm rates from naturally occurring radioactive material. Various implementations of energy windowing have been tested and documented by industry and at Pacific Northwest National Laboratory, and are available in commercial RPMs built by several manufacturers. Moreover, energy windowing is being used in many deployed RPMs to reduce nuisance alarms and improve operational sensitivity during the screening of cargo. This paper describes energy windowing algorithms and demonstrates how these algorithms succeed when applied to “controlled” experimental measurements and “real world” vehicle traffic data.     

Influence of temperature and strain rate on cohesive properties of a structural epoxy adhesive

Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive are studied experimentally. Two parameters of the cohesive laws are given special attention: the fracture energy and the peak stress. Temperature experiments are performed in peel mode using the double cantilever beam specimen. The temperature varies from −40 to + 80°C. The temperature experiments show monotonically decreasing peak stress with increasing temperature from about 50 MPa at −40°C to about 10 MPa at + 80°C. The fracture energy is shown to be relatively insensitive to the variation in temperature. Strain rate experiments are performed in peel mode using the double cantilever beam specimen and in shear mode, using the end notch flexure specimen. The strain rates vary; for peel loading from about 10⁻⁴ to 10 s⁻¹ and for shear loading from 10⁻³ to 1 s⁻¹. In the peel mode, the fracture energy increases slightly with increasing strain rate; in shear mode, the fracture energy decreases. The peak stresses in the peel and shear mode both increase with increasing strain rate. In peel mode, only minor effects of plasticity are expected while in shear mode, the adhesive experiences large dissipation through plasticity. Rate dependent plasticity, may explain the differences in influence of strain rate on fracture energy between the peel mode and the shear mode.     

The temperature of a vibrated granular gas

The temperature of a granular medium is defined, in a manner analogous to that of a molecular gas, as the root mean squared kinetic energy of the grains. Using a novel two-layer granular experiment, we have made a systematic study of the granular temperature as a function of driving parameters in order to determine whether the behavior of the granular temperature is truly analogous to the temperature of a molecular gas. By examining the behavior of this particular system in detail, where two fluctuating granular media are in thermal contact, we also suggest general conditions under which such analogies can be extended to other driven systems.     

The development of a novel temperature indicator

The δ-ferrite transformation characteristics of a series of specially made experimental duplex stainless steels have been studied. The ferrite content of these steels changes with time and temperature and this special property is used to develop an effective temperature indicator, i. e. if the time of exposure is known the change in ferrite content in these steels can be used to indicate the average temperature over this period.

A Feritscope is used to measure the ferrite content, a measurement which can be performed on site in a matter of seconds. Further advantages of using stainless steel are that it is corrosion resistant, tough, ductile and only a small sample (e.g. 6 mm diameter x 2 mm thick) is required for reproducible measurement.     

The synthesis and optical property of solid-state-prepared YAG:Ce phosphor by a spray-drying method

Ce³⁺-activated yttrium aluminum garnet (Y₃Al₅O₁₂:Ce, YAG:Ce) powder as luminescent phosphor was synthesized by the solid-state reaction method. The phase identification, microstructure and photoluminescent properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), absorption spectrum and photoluminescence (PL) analysis. Spherical phosphor particle is considered better than irregular-shaped particle to improve PL property and application, so this phosphor was granulated into a sphere-like shape by a spray-drying device. After calcinating at 1500 °C for 0, 4, and 8 h, the product was identified as YAG and CeO₂ phases. The CeO₂ phase content is decreased by increasing the calcination time or decreasing the Ce³⁺ doping content. The product showed higher emission intensity resulted from more Ce³⁺ content and larger grain size. The product with CeO₂ was found to have lower emission intensity. This paper presents the crystal structures of Rietveld refinement results of powder XRD data.