Crystalline matrices

In the later 1920 s, physicists, rightly flushed with their successes with interpreting the rich, sharp spectra of atoms and gas phase ions, sought to extend their reach to the broader (and fewer) absorption bands that eharacterize the spectra of ions in crystalline matrices. These bands occur at utterly different frequencies to those of the corresponding free ions so that there is no similarity at all between the spectra of free ions and of those in ionic or covalent lattices. 

NS Sariciftci, U Lemmer, D Vacar, AJ Heeger, and RAJ Janssen, Polarized photoluminescence of oligothiophenes in nematic liquid crystalline matrices, Adv. Mater., 8 651-653, 1996. 

The comparison of sensitivity and limits of detection achievable in ILMs and crystalline matrices have led to inconsistent results in different studies. For the measurement of peptides, a number of groups have reported comparable or even increased sensitivities in ILMs in positive [16,50] or negative ion mode [39], whereas others have reported decreased sensitivities [40]. For oligonucleotides [41], phospholipids [48], again increased sensitivities have been reported. For low-molecular weight analytes like sugars, decreased [40] or comparable limits of detection have been found [38]. 

Despite the use of balancing mechanisms of ion extraction, for example, delayed extraction, larger inhomogeneities frequently found in slowly grown crystalline matrix preparations are known to influence the mass accuracies. The highly homogeneous sample surfaces achievable in ILMs can drastically reduce these problems upon conversion of the crystalline matrices into ILMs [45]. 

Low- and intermediate-level waste is currently converted to cement and bitumen waste forms, but the existing trend is toward an increase in the radiation safety levels and reliability of immobilization. From this point of view, LILW should also be incorporated in vitreous and crystalline matrices. Current Russian and US experience on vitrification of such waste demonstrates the potential of the melting/vitriflcation process. Major advantages of vitrification over bituminization and cementation are a greater waste volume reduction, higher productivity, and higher durability of the final product. 

Glagovsky, E. M., Yudintsev, S. V., Kuprin, A. V., Pelevin, L. P., Konovalov, E. E., Velichkin, V. I. Myasoedov, B. F. 2001. A study of actinide crystalline matrices produced by self-sustaining high-temperature synthesis. Radiochemistry, 43, 557-562 (in Russian). 

However, such is not the case here, and, in fact, we will soon appreciate the amount of extensive studies already made on the absorption and fluorescence spectra of the rare earth ions, both in crystalline matrices and in solution. 

From a practical point of view, these compounds are models of crystalline matrices for nuclear waste disposal. One such storage material is SYNROC, a synthetic mineral whose major constituents are the complex oxides hollandite, zirconolite, and perovskite. We have chosen perovskite as a model structural family because of its efficient packing and its accommodation of a wide range of cations, both in size and oxidation state (5). 

The mechanical response of composites, as shown in these exploratory studies, indicates dependence on the ease with which fracture can occur between fibers, yarns, and plies. Poorly crystallized matrices result in composites that are strong and stiff but with little yield so that failure occurs catastrophically. In contrast, more crystalline matrices seem to be not quite as strong and to have a lower effective modulus, but their increased strain capability ensures that failure is not catastrophic the composited strength decays gradually as further strain is applied. Thus, the energy required for total failure is increased, and the composite with more crystalline matrix is more tolerant of defects or stress risers. 

At elevated pressures, gases adsorb to crystalline matrices or dissolve in amorphous solids,... 

So, it is expedient to separate them from the HLW that may be vitrified and incorporate these actinides into crystalline matrices (nuclear waste forms) or fabricate them into solid targets for transmutation in nuclear reactors or accelerators. There are a variety of processes for processing and partitioning the actinides - TRUEX (USA, Japan, Russia), DIAMEX (USA, Japan, EEC), TRPO (PRC), SANEX (USA, EEC, PRC), are under development [6]. The basic process in these technologies is extraction (or precipitation) of actinides from HLW solutions using special reagents. These methods provide for the separation of a high-actinide fraction or joint extraction of actinides, rare earths, and zirconium. The proportion of elemental concentrations in typical fractions is (in wt.%) actinides - 10-15, rare earths - 60-65, zirconium - 20-25 [7]. 

Kelvin (the zero point motion). This latter effect is explained by quantum mechanics, and it can in turn explain absorption features of impurities in crystalline matrices. The presentation of the fundamental vibrational modes of crystals is based on the harmonic approximation, where one only considers the interactions between an atom or an ion and its nearest neighbours. Within this approximation, an harmonic crystal made of N ions can be considered as a set of 3N independent oscillators, and their contribution to the total energy of a particular normal mode with pulsation ivs (q) is ... 

In the present work, we consider the two approaches for synthesis of nanoparticles designed for metal particles and being in the progress for ultraflne semiconductors. They allow to fabricate nanocomposites of the type nanoparticles-in-dielectrics with amorphous and crystalline matrices. The first one is based on the sol-gel technique producing dielectric silica films with nanoparticles incorporated within silica matrix [1]. Nanoparticles provide an optical response of the material due to the plasmon resonance [2] with variable spectral position and band shape. In the second approach nanoparticles are produced within the crystalline zeolite matrices which stabilize both the few-atomic clusters (e.g., Agg) and metal particles in the size range of 1-20 nm [3], Chemical routes of their synthesis admit easy control of size and optical properties. The metal nanoparticles in zeolites can be transformed into semiconductors without destroy of the zeolite matrix and with incorporation of zeolite microcrystals into transparent silica films. This construction... 

H20 leading to a linear trimer, or between two dimers 2 [Si207] + 2 H+ —i- [Si40i3] °" + H20 leading to a linear tetramer. Both anions have been isolated in crystalline matrices. The linear trimer is found in the compound... 

X 10 cm This study provided initial proof of concept for the use of liquid crystalline matrices as on-demand stimuli-responsive systems for hydrophilic drugs. 

In vitro release studies were carried out first to establish the influence of the liquid crystalline symmetry on the release behavior. Figure 12.29a illustrates the drug release profiles from the liquid crystalline matrices, plotted as a percentage of the released drug against time. As can be observed, the release from Iniim is much more rapid and is nearly completed after 20 h at this time, Hn has not yet released half of the initially loaded drug. 

Solid samples generally contain some adsorbed and/ or absorbed water. In the case of inorganic materials, drying is carried out in an oven at 105-110°C for a few hours, although lower temperatures need to be used if the sample contains volatile components. On the other hand, higher temperatures may be required to remove water trapped within crystalline matrices. 

The optical absorption or excitation lineshape of dopant molecules in crystalline matrices at low temperatures has been investigated both experimentally and theo-... 

Tn denotes the dephasing time of the optical transition, T the lifetime of the excited state (fluorescence hfetime) and the pure dephasing time. At low temperatures T is essentially independent on temperature while shows a strong dependence on temperature. The actual value of at a given temperature depends on the excitation of low frequency modes (phonons, librations) that couple to the electronic transition of the chromophore. In crystalline matrices at low temperatures (T <2 K) Tl approaches infinity as host phonons and local modes are essentially quenched and the linewidth is solely determined by the lifetime contribution. 

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