X-ray induced luminescence

Godmanis 1, Hohenau W (1989) On the nature of afterglow of the X-ray-induced luminescence in crystalline and glassy Si02. Physica Status Solid A Appl Res 111 335-343... 

X-ray-induced luminescence (XL) and luminescence induced by other ionizing radiation are presented in fig. 1 by transition 1. It will, however, also produce transitions like 2 and 5. This will jdeld more complex excitation and emission spectra. 

Luminescence of Eu and Eu has been found in the X-ray excited luminescence spectra of synthetic leucophane activated by Eu (Prokofiev et al. 1982 Eig. 5.17), while in natural samples only Eu " " was detected. Laser-induced time resolved luminescence under 532 nm excitation enables us to detect clear lines of Eu " " with the strongest Dq- Fq electron transition at 573 nm (Eig. 4.25). 

Fig. 8.3 (a-d) Laser-induced luminescence spectra of diamonds with different X-Rays excited luminescence intensity under excitation by 215 nm... 

The book deals mainly with theoretical approach, experimental results and their interpretation of laser-induced time-resolved spectroscopy of minerals in the wide spectral range from 250 to 2000 nm, which enables to reveal new luminescence previously hidden by more intensive centers. Artificial activation by potential luminescence centers has been accomplished in many cases, which makes the sure identification possible. The mostly striking example is mineral apatite, which has been extremely well studied by many scientists using practically all known varieties of steady-state luminescence spectroscopy photoluminescence with lamp and laser excitations. X-ray excited luminescence, cathodoluminescence, ionolumi-nescence and thermoluminescence. Nevertheless, time-resolved spectroscopy revealed that approximately 50 % of luminescence information remained hidden. The mostly important new information is connected with luminescence of trivalent... 

Figure 1. Left Panel X-ray-induced emission spectra of LaC13 0.57% Ce between 135 and 400 K. (from ref [1]). Right Panel X-ray excited optical luminescence spectramofLaBr3 0.5%, 4%and 10% Ce3 at room temperature. The inset shows the spectrum of pure LaBr3 Ce at 100 K, from ref [10]...

According to Ludwig (1968), there is a some similarity between UV- and high-energy-induced luminescence in liquids. In many cases (e.g., p-ter-phenyl in benzene), the luminescence decay times are similar and the quenching kinetics is also about the same. However, when a mM solution of p-terphenyl in cyclohexane was irradiated with a 1-ns pulse of 30-KeV X-rays, a long tail in the luminescence decay curve was obtained this tail is absent in the UV case. This has been explained in terms of excited states produced by ion neutralization, which make a certain contribution in the radiolysis case but not in the UV case (cf. Sect. 4.3). Note that the decay times obtained from the initial part of the decay are the same in the UV- and radiation-induced cases. Table 4.3 presents a brief list of luminescence lifetimes and quantum yields. 

Under lamp excitation tourmaline is practically non-luminescent, while under X-ray excitation it exhibits impurity luminescence from Fe centered at 700-750nm and Mn + centered at 560-570nm (Kusnetsov and Tarashchan 1988). The natural tourmaline in our study consisted of four samples. The laser-induced time-resolved technique enables us to detect Cr + emission centers (Fig. 4.58). 

Thorite and orangite (orange thorite) have a tetragonal structure and are isostructural with zircon. Steady-state spectra under X-ray and laser (337 nm) excitations are connected with REE " ", namely Sm " ", Tb ", Dy " " and Eu ". Reabsorption lines of Nd " have been also detected (Gorobets and Rogojine 2001). Laser-induced time-resolved luminescence enables us to detect Eu " and uranyl emission centers (Eig. 4.70). 

Fig. 5.16. Laser-induced luminescence of barite 1 - after heating at 600 °C while violet luminescence of evidently Eu " appears 2 - after X-ray irradiation of the heated sample where blue shoulder appears, supposedly connected with Eu+ (Gaft and Rudenkova 1993)...

SIMS (61,64,86), microscopy (65), XPS (56), electron microprobe techniques (14,66), electron paramagnetic resonance (EPR) (67) and luminescence experiments (68) have been successfully employed to probe and study V mobility and reactivity on a catalyst surface. TEM, STEM and energy dispersive X-ray emission (EDX) measurements have indicated that V interaction with REY-crystals induced vanadate clusters formation (65). Vanadium was also found capable of reacting with rare-earths outside the zeolite cavities to form LaVQ4... 

The mechanisms of the photostimulated luminescence of Eu2+-doped fluorohalides have been extensively studied. In BaBrF Eu an excess of fluorine favours the formation of F centres in bromine sites. This results in a red shift of the absorption induced by X-rays which increases the luminescence yield for stimulation by a He—Ne laser at 633 nm [69], Various interpretations have been proposed both about the nature of the hole-trapping centre and the electron-hole recombination mechanism [70], It was initially assumed that holes are trapped by Eu2+, leading to the formation of Eu,+ [71]. However after long X-ray irradiation no change in the EPR signal of Eu2+ was observed and the luminescence of Eu3+... 

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-induced and x-ray fluorescence are important analytical techniques (see... 

Chao Y, Krishnamurthy S, Montalti M, lie LH, Houlton A, Horrocks BR, Kjeldgaard L, Dhanak VR, Hunt MRC, Siller L (2005) Reactions and luminescence in passivated Si nanocrystallites induced by vacuum ultraviolet and soft-X-ray photons. 1 Appl Phys 98 044316... 

A number of less commonly used analytical techniques are available for determining PAHs. These include synchronous luminescence spectroscopy (SLS), resonant (R)/nonresonant (NR)-synchronous scan luminescence (SSL) spectrometry, room temperature phosphorescence (RTP), ultraviolet-resonance Raman spectroscopy (UV-RRS), x-ray excited optical luminescence spectroscopy (XEOL), laser-induced molecular fluorescence (LIMP), supersonic jet/laser induced fluorescence (SSJ/LIF), low- temperature fluorescence spectroscopy (LTFS), high-resolution low-temperature spectrofluorometry, low-temperature molecular luminescence spectrometry (LT-MLS), and supersonic jet spectroscopy/capillary supercritical fluid chromatography (SJS/SFC) Asher 1984 Garrigues and Ewald 1987 Goates et al. 1989 Jones et al. 1988 Lai et al. 1990 Lamotte et al. 1985 Lin et al. 1991 Popl et al. 1975 Richardson and Ando 1977 Saber et al. 1991 Vo-Dinh et al. 1984 Vo- Dinh and Abbott 1984 Vo-Dinh 1981 Woo et al. 1980). More recent methods for the determination of PAHs in environmental samples include GC-MS with stable isotope dilution calibration (Bushby et al. 1993), capillary electrophoresis with UV-laser excited fluorescence detection (Nie et al. 1993), and laser desorption laser photoionization time-of-flight mass spectrometry of direct determination of PAH in solid waste matrices (Dale et al. 1993). 

Details of the neutralization process following radiation-induced primary charge separation may be examined via the medium of ultrafast techniques now employed in studies of luminescence decay processes. As an example, the form of luminescence decay curves of dilute organic scintillator in aliphatic hydrocarbon solution excited by x-ray pulses of about 0.5-1.0 nsec, duration is attributed (in previous papers) to neutralization processes involving ions. The relation, t cc r3, for the time required for neutralization of an ion pair of initial separation r, when applied to such curves, leads to a distribution function of ion-pair separations. A more appropriate and desirable approach involves solution of a diffusion equation (which includes a Coulomb interaction term) for various initial conditions. Such solutions are obtained by computer techniques employed in analogy to corresponding electrical networks. The results indicate that the tocr3 law affords a fair description of the decay if the initial distribution can be assumed to be broad. 

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