UV-visible / luminescence

Gaft M, Reisfeld R, Panczer G, Dimova M (2008b) UV-visible luminescence of Nd in minerals. J Alloy Comp 451 56-61... 

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. 

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

Thus, although the colour of sparks is dependent upon flame temperature and may be similar to that of black body radiation, the overall colour effect can include contributions from atomic line emissions, from metals (seen in the UV and visible regions of the electromagnetic spectrum), from band emissions from excited oxide molecules (seen in the UV, visible and IR regions) and from continuum hot body radiation and other luminescence effects. So far as black body radiation is concerned, the colour is known to change from red (500 °C glowing cooker... 

Mixtures of phosphine and oxygen, both above and below the explosion limits, subjected to flash photolysis show, in the spectra, the presence of PH-, OH- and PO-radicals as well as the PH2-radical Eiuiing the reaction of atomic oxygen with phosphine visible luminescence up to 3600 A and UV emission were observed, which were attributed to the partial processes ... 

Thulium displays in minerals an intense UV and blue visible luminescence with a line spectrum near 360 and 450 nm, correspondingly. They are connected with electron transitions from different excited levels D2 and at 360-365 and 450-455 nm. The liuninescence of Tm " is more easily detected in time-resolved spectra with a narrow gate, because it usually has a relatively short decay time. The UV Hne usually has a much shorter decay time compared with the blue line. Different decay times from these levels are evidently connected with nonradiative relaxation due to the presence of high frequency vibrations in the lattice. The best excitation is at 355 nm, which is connected with transition... 

All of these complexes display a strong visible luminescence under UV excitation, which is sensitive to the interaction of the gold atoms with the mercury centers. Thus in Hg(-C,C-C6F4 ]3([AuC(0-R)=NR ]3)2 and Hg (p.-C,C-C6F4)3([Au(p,-C2,N3-Rim)]3)2 ra an increase of the intensity upon coordination of mercury to the starting gold materials was observed. 

The wide tuning of the electronic properties of [2]catenates, as observed from electrochemistry and UV-visible absorption, causes a nice modulation of the luminescence properties in CH2CI2 solution. On changing the metal ion, the luminescence bands of this catenate family are tuned throughout the whole visible spectral region [60] (Figure 15). The luminescence data at 298 and 77 K in CH2CI2 are reported in Table 9. 

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