X-ray luminescence

X-ray luminescence occurs where X-rays supply the energy. 

Diamond luminescence was studied mainly with the two following aims to carry out a fundamental investigation of its physical properties and to determine the optimal conditions for luminescent sorting of diamond bearing rocks. For the first task, diamond photoluminescence was studied at liquid nitrogen temperature at which luminescence centers are marked by characteristic zero-phonon fines and are much more informative then at room temperature. For the second task, were diamond is one of the first minerals for which luminescence sorting was used, liuninescence properties should be studied at 300 K. In the first stages it was established that X-ray luminescence of the A-band... 

At the present time new deposits have been discovered which contain diamonds without luminescence under X-ray excitation. Sometimes the portion, which is unrecoverable in X-ray luminescent sorters, is big enough to warrant the development of a new sorting method. The luminescence spectra were investigated under excimer (193,222,248 and 308 nm), nitrogen (337 nm) and dye laser (340-360 nm) excitations (Fig. 8.2). 

X-ray excited steady-state luminescence has been checked as a distinctive feature for the phosphorites, Karatau (Gorobets et al. 1997a). Sedimentary apatite (francolite) is not luminescent under X-ray excitation and red Mn " luminescence of dolomite was employed. As a result, concentration of MgO in the accepted fraction was lowered from 5.0% to 2.4%. The use of this method is limited because in many cases the X-ray luminescence of dolomite is very low or non-existent. Besides that, other minerals without luminescence come together with the accepted phosphate fraction, including sihceous shale, which is harmful for the following deep beneficiation. Thus new methods have to be developed for detection and content evaluation of dolomite in Florida phosphates on moving belt conveyors. 

Magnesium Tungstate. [CAS 1357.3-11-0. (magnesium w-ollranraie) Mg WO., while crystals. D 5.66. soluble in acids, insoluble in water and alcohol, formed by interaction of solutions of magnesium sulfate and ammonium tungstate. Use Fluorescent screens for X-rays, luminescent paint. 

Finally, X rays of a certain X can specifically excite X-ray luminescence of the sample. Thus, Cu-Ka line will excite iron atoms, and Mo-K those of yttrium, producing a strong parasitic background which (imlike Bragg scattering) does not decrease with the increase of the Bragg angle - a most unwelcome complication. 

Depending on the excitation method used, luminescence techniques are divided into photoluminescence excited by photons, cathodoluminescence generated under the action of cathode rays, X-ray luminescence excited by X-rays, candoluminescence generated under the action of heat, and sonoluminescence excited by ultrasound. Emission generated under the action of a stream of ions from alkali metals in vaccum is called ionoluminescence radiation which atoms emit on optical excitation in plasma is known as atomic fluorescence chemiluminescence is the emission of radiation generated by the energy of chemical reactions, it does not require an external excitation source. The excitation source needed in each particular case is chosen on the basis of this classification. 

Luminescence is a phenomenon originating from the emission transition of ions, molecules or a crystal lattice from an excited electronic state to a ground state or a state with lesser energy. Depending on the mode of excitation, several types of luminescence can be distinguished such as photo-, cathodo-, thermo-, chemo-, tribo-, crystallo-, bio- and X-ray luminescence. 

Coxon PR, Newman M, Hunt MRC, O Farrell N, Horrocks BR, Poolton NRJ, Siller L (2012) DNA-modified silieon nanocrystals studied by X-ray luminescence and X-ray absorption spectroscopies observation of a strong infra-red luminescence band. J Appl Phys 111 054311 Credo GM, Mason MD, Buratto SK (1999) External quantum efficiency of single porous silicon nanoparticles. Appl Phys Lett 74 1978-1980... 

The sensitivity of the luminescence IP s in the systems employed here decreases with increasing x-ray energy more strongly than in the case of x-ray film. Therefore, this phenomenon must be compensated by using thicker lead front and back screens. The specific contrast c,p [1,3] is an appropriate parameter for a comparison between IP s and film, since it may be measured independently of the spatial resolution. Since the absorption coefficient p remains roughly constant for constant tube voltage and the same material, it suffices to measure and compare the scatter ratio k. Fig. 2 shows k as a function of the front and back screen thickness for the IP s for 400 keV and different wall thicknesses. The corresponding measured scatter ratios for x-ray films with 0,1 mm front and back screens of lead are likewise shown. The equivalent value for the front and back screen thicknesses is found from the intersection of the curves for the IP s and the film value. 

Fluorescence and phosphorescence are types of luminescence, ie, emission attributed to selective excitation by previously absorbed radiation, chemical reaction, etc, rather than to the temperature of the emitter. Laser-iaduced and x-ray fluorescence are important analytical techniques (see... 

Tungsten is usually identified by atomic spectroscopy. Using optical emission spectroscopy, tungsten in ores can be detected at concentrations of 0.05—0.1%, whereas x-ray spectroscopy detects 0.5—1.0%. ScheeHte in rock formations can be identified by its luminescence under ultraviolet excitation. In a wet-chemical identification method, the ore is fired with sodium carbonate and then treated with hydrochloric acid addition of 2inc, aluminum, or tin produces a beautiful blue color if tungsten is present. 

Several instmmental methods are available for quantitative estimation of from moderate to trace amounts of cerium in other materials. X-ray fluorescence is widely available, versatile, and suitable for deterrninations of Ce, and any other Ln, at percent levels and lower in minerals and purer materials. The uv-excited visible luminescence of cerium is characteristic and can be used to estimate Ce content, at ppm levels, in a nonluminescing host. X-ray excited optical luminescence (15), a technique especially appropriate for Ln elements including cerium, rehes on emissions in the visible, and also measures ppm values. Atomic emission spectrometry is appHcable to most lanthanides, including Ce (16). The precise lines used for quantitative measurement must be chosen with care, but once set-up the technique is suitable for routine analyses. 

Deng et al. (2004a,b) prepared the crystals of the spent obelin (W92F mutant from O. longissima) that had been luminesced with Ca2+, and successfully obtained the X-ray structure of apoobelin as an important information in elucidating the mechanism of the luminescence reaction. 

Molecular characteristics of luciferase. A molecule of the luciferase of G. polyedra comprises three homologous domains (Li et al., 1997 Li and Hastings, 1998). The full-length luciferase (135 kDa) and each of the individual domains are most active at pH 6.3, and they show very little activity at pH 8.0. Morishita et al. (2002) prepared a recombinant Pyrocystis lunula luciferase consisting of mainly the third domain. This recombinant enzyme catalyzed the light emission of luciferin (luminescence A.max 474 nm) and the enzyme was active at pH 8.0. The recombinant enzyme of the third domain of G. polyedra luciferase was crystallized and its X-ray structure was determined (Schultz et al., 2005). A -barrel pocket putatively for substrate binding and catalysis was identified in the structure, and... 

The Preparation and X-ray-excited Intrinsic Scintillation Luminescence Properties of Ba3BP30i2, BaBPOs and Ba3BP07 [14, 15]... 

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