Luminescent impurities

Interactions in Solid-Surface Luminescence Temperature Variation. Solid-surface luminescence analysis, especially solid-surface RTF, is being used more extensively in organic trace analysis than in the past because of its simplicity, selectivity, and sensitivity (,1,2). However, the interactions needed for strong luminescence signals are not well understood. In order to understand some of the interactions in solid-surface luminescence we recently developed a method for the determination of room-temperature fluorescence and phosphorescence quantum yields for compounds adsorbed on solid surfaces (27). In addition, we have been investigating the RTF and RTF properties of the anion of p-aminobenzoic acid adsorbed on sodium acetate as a model system. Sodium acetate and the anion of p-aminobenzoic acid have essentially no luminescence impurities. Also, the overall system is somewhat easier to study than compounds adsorbed on other surfaces, such as filter paper, because sodium acetate is more simple chemically. 

The natural fluor-apatites in our study consisted of 75 samples from a variety of geologic environments. Concentrations of potential luminescence impurities in several samples are presented in Table 4.4. 

The fluorite in our study consisted of 40 samples from different environments. Concentrations of luminescence impurities in several samples are given in Table 4.6. By using laser-induced time-resolved spectroscopy we were able to detect and ascribe the following emission centers Eu +, Ce ", Gd +, Sm +, Dy3+, Eu +, Pr +, Er +, Tm +, Ho +, Nd +, Mn + and the M-center (Figs. 4.10-4.12). 

Datolite is caldiun borosilicate with a monoclinic structure (2/m) and space group P2i/c. It consists of superimposed complex sheets of linked oxygen and O, OH tetrahedra around silicon and boron atoms respectively the Si04 and B(0,0H)4 tetrahedra alternate, forming rings of four and eight tetrahedra. The natural datolite in our study consisted of seven samples from a variety of geologic environments. Concentrations of potential luminescence impurities in one sample are presented in Table 4.8. 

The natural barite in our study consisted of twenty-five samples of different origin. Concentrations of potential luminescence impurities in several samples are presented in Table 4.11. For the correct interpretation of the luminescent bands, artificial barite standards have been investigated, as nominally pure, and activated. The laser-induced time-resolved technique enables us to detect Ag+, Bi +, Bi, Eu, Ce +, Nd +, (U02) and several still not identified emission centers (Figs. 4.29-4.31). 

Hydrozincite is anhydrous carbonates. The crystalline system is monoclinic-prismatic with the space group C2/m. The structure is composed of Zn in both octahedral and tetrahedral coordination, in the ratio 3 2. The octahedral Zn atoms form part of a C6 type sheet with holes. The octahedral Zn atoms occur above and below these holes. The natural hydrozincite in our study consisted of three samples. Concentrations of potential luminescent impurities are presented in Table 4.13. The laser-induced time-resolved technique enables us to detect Pb center (Fig. 4.37). 

Table 4.15. Concentrations of potential luminescent impurities (ppm) in several zircon samples ...

The mineral matrix is formed chiefly by La " or Ce ". The last one is widely regarded as the luminescence impurity center, but in rare-earth bearing minerals it is subjected to concentration quenching because of strong exchange... 

You should also explore the issue of background signal due to dark noise, scattered light or (possibly) luminescent impurities in the cuvette or water. 

Nonluminescent impurities may also interfere by quenching analyte fluorescence. They may be removed much as luminescent impurities are removed. 

In this paper we report on the identification of the luminescent impurity carbonyl species in two of the most light-sensitive polyolefins, polypropylene and poly(4-methylpent-l-ene) and examine the behavior of these groups during irradiation under sunlight-simulated conditions. 

The natural hydrozincite in our study consisted of three samples. Concentrations of potential luminescent impurities are presented in Table 4.13. Laser-induced time-resolved technique enables to detect Pb " center (Gaft et al. 2002a) (Fig. 4.85a, b). 

Table 4.13 Concentrations of rare-earth elements and other potential luminescent impurities in hydrozincite samples (ppm)...

Mineral matrix is formed chiefly by La " or Ce ". The last one is widely met as luminescence impurity center, but in rare-earth bearing minerals it is subjected to concentration quenching because of strong exchange interaction of outer 5d orbitals of neighboring Ce " ions. Hereby its luminescence is not observed in REE minerals. From the other side, other trivalent REE can achieve some concentrations without quenching of luminescence, because outer electron shells, such as 5s and 5p , shield their inner 4f-4f transitions. 

The main peculiarity ofXAS is that it can provide the local atomic order around chosen chemical species. No long-range order is required and this makes XAS an ideal technique for the determination of sites ofimpurities (10 -10 Ppm) in different matrices. Atypical issue discussed in the literature is on the local order aroimd luminescent impurities in glasses for optoelectronic applications. Indeed, a typical aU optical device should consist of optical guides and active components (amplifiers, switches,...) of minimum size. The sol-gel route, permitting the deposition of a thin film on a substrate, appears to be an ideal technique for the fabrication of such devices (Orignac, 1999 Stone, 1996). 

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