Luminescence rare-earth elements

Most of the electronic spectroscopy in minerals can be interpreted by the well-known ligand field theory. The main luminescence centers in minerals are transition and rare-earth elements. The ground and excited levels in these cases are d and / orbitals, while d-d and d-f emission transitions are subjected to strong influence from nearest neighbors, so called ligands. The basic notion of... 

Leucophane is a relatively rare berylhum silicate. Of interest are the trace amounts of rare earth elements in its chemistry, especially cerium which substitutes for some calcium. Its true symmetry is triclinic, pedion class which is the lowest symmetry possible in a three dimensional system. The only symmetry element is translational shift as it lacks any mirrors, rotations, or even a center. The symmetry is noted by a 1. Ce ", Eu +, Sm +, Dy +, Tb ", Nd " " and Mn " centers characterize steady-state luminescence spectra of leucophane (Gorobets and Rogojine 2001). Time-resolved luminescence spectra contain additionally Eu and Tm " " centers (Fig. 4.25). 

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

Another group of lines is detected in the titanite luminescence spectrum, which may be considered as connected with the Nd " " emission. Those lines at 589, 658, 743 and 846 nm are especially strong in the luminescence spectra with a narrow gate excited by Aex = 532 nm (Fig. 4.34b). Such a combination of emission lines with relatively short decay times is very unusual for minerals and may not be easily connected to any rare-earth element traditional for luminescence in the visible range. If we were to consider the possible connection with the visible emission of Nd " ", the detected lines correspond very well, for example, to electron transitions from 67/2 level to %/2> fii/2> fi3/2 and Ii5/2 levels. 

The rare earth elements are different from other elements because the optical transitions between levels of the fn configuration are inherently very sharp-lined and have well-resolved structure characteristic of the local crystal fields around the ion. In minerals, this characteristic provides an excellent probe of the local structure at the atomic level. Examples will be shown from our work of how site selective laser spectroscopy can be used to determine the thermal history of a sample, the point defect equilibria that are important, the presence of coupled ion substitution, the determination of multiple phases, and stoichiometry of the phase. The paper will also emphasize the fact that the usefulness and the interpretation of the rare earth luminescence is complicated by the presence of quenching and disorder in mineral samples. One in fact needs to know a great deal about a sample before the wealth of information contained in the site selective luminescence spectrum can be understood. 

Other Minerals Up to this point, reference has been made to other luminescing phases within meteorites but in all cases no systematic studies have been reported to 1) determine the cause of the CL or 2) to relate the CL to the genesis of the mineral or meteorite. The following comments are made to draw attention to the possible significance of CL observations in other meteoritic minerals most observations are from the author s personal experience and have not been documented. Oldhamite is a rare mineral in the enstatite chondrites but is known to carry appreciable quantities of rare earth elements (REE). The CL spectra have not been studied in detail but visual CL is yellow and a CL emission at 580nm was reported (H) but with rapid intensity change under the electron beam. A REE activator of the CL is possible. Hibonite is a relatively common... 

In this connection, the application of inorganic dielectric nanocrystals based on the activated compounds of rare-earth elements seems to be prospective. Such compounds are non-toxic and have intensive luminescence, narrow spectral lines and high photostability. Furthermore, these nanocrystals can be obtained in aqueous solutions that is very important for biological applications [3]. 

Kuznetsova, V. V. et al. Applications of Luminescence for the Control and Analysis of Materials Containing Rare Earth Elements, Minsk, Inst. Fis. AN BSSR, 1970... 

Rare earth element doped alkaline earth sulfides are employed in luminescence-based devices like thin film electroluminescent displays [119,120] and devices for optical data storage [121]. Strontium sulfide, SrS, thin films have been prepared by atomic layer epitaxy from [Sr(tmhd)2] (tmhd" 7) in the presence of HiS [122]. Additionally, solid sources have been employed in a comparable CVD approach [122b]. 

The fluorescence properties of several europium and samarium ) -diketonates have been measured and assignments of the transitions made. Rare-earth element hexafluoroacetylacetonates with amino-acids have also been reported to fluoresce. The luminescence of the heptafluoroheptane-2,4-dione complexes of Sm, Eu, and Tb has been measured in dilute ethanol at pH8 and 610nm mixed-ligand complexes with 1,10-phenanthroline exhibited an enhanced luminescence. Photolysis of the Tb chelate of 2,2,6,6-tetramethylheptane-3,5-dione has been examined at 311 nm in various alcohols, and loss of one -diketone ligand found to be the primary photochemical step. A linear correlation was demonstrated between the quantum yield of dissociation of the complex and the formation constant of the complex-alcohol adduct. 

O. N. Gorshkov, I. A. Grishin, E. B. Intushin, Y. E. Elliev, Y. I. Chigirinskiy, in Proceedings of International Symposium on Photo- and Electro luminescence of rare-earth elements in semiconductors and dielectrics (St. Petersburg, 2001) 17. 

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