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The x-ray-induced ‘‘blue’’ emission from commercially available, high-quality synthetic quartz has been studied between 80 and 300 K. Three overlapping bands, each having a different quenching temperature, have been experimentally resolved in the as-grown crystals. These bands peak at 440, 425, and 380 nm; their half-widths are 0.64, 0.75, and 0.92 eV; and they thermally quench in the 120–160, 170–210, and 220–270 K regions, respectively. An intense electron irradiation at room temperature or an electrodiffusion (sweep) in a hydrogen atmosphere eliminates the band at 380 nm. Our results suggest that the 380-nm band arises from recombination of an electron with a hole trapped adjacent to an alkali-compensated aluminum ion (i.e., an Al–M+ center). The origins of the bands at 440 and 425 nm remain unknown. As an application of these results, a screening test is described which could assist quality control during selection of quartz bars for use in precision frequency control devices.

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An electron-nuclear double resonance (ENDOR) study at 20 K of the [AlO,]O trapped-hole center i n u-quartz gives the principal axes and principal values of the 27Al hyperfine and quadrupole matrices. These are in substantial agreement with previous ESR results obtained by Nuttall and Weil. A model involving both dipole-dipole interactions and the admixing of unpaired spin into aluminum 3p-type orbitals is used t o explain the small anisotropic 27Al hyperfine matrix components. The "best fit" with this model results in 3.7% of an unpaired spin in aluminum 3p-type orbitals and a 0.188 nm distance from the aluminum ion to the oxygen ion containing the trapped hole.Eine Elektronen-Kern-Doppelresonanz (ENDOR) Untersuchung bei 20 K des [A1OJO-Zentrums mit eingefangenem Loch in a-Quartz ergibt die Hauptachsen und -werte der 27Al-Hyperfeinund Quadrupolmatrizen. Sie sind in wesentlicher Ubereinstimnng mit friiheren ESR-Ergebnissen von Nuttall und Weil. Ein Modell, das sowohl Dipol-Dipol-Wechselwirkung als auch die Beimiscliung von ungepaartem Spin in Aluinmium-3p-Orbitale einschlieBt, wird zur ErklLrung der geringen anisotropen 27Al-Hyperfeinmatrixkomponenten herangezogen. Die ,,beste Anpassung" an dieses Modell fiihrt zu 3,7% eines ungepaarten Spins in den Aluminium-3p-Orbitalen und zu einem Abstand von 0,188 nm des Aluminiumions vom Sauerstoffion, das das eingefangene Loch enthLlt .

Paramagnetic resonance spectra of 4d1 (Nb4+ and Mo5+) and 5d1 (W5+) ions at substitutional cation sites in single crystals of tetragonal GeO2 have been studied at 92 K. Spin-Hamiltonian parameters obtained from hyperfine and superhyperfine (shf) structures are reported and compared with previously reported results for these ions and for V4+ (3d1), in rutile-structure GeO2, TiO2, and SnO2. Analysis of superhyperfine interactions with these nd1 impurity cations in GeO2 indicates that the unpaired spin is highly delocalized into nearest-neighbor ligand cations. On the basis of an LCAO-MO treatment, delocalization probabilities are inferred from measured shf interactions for these impurities; for each, the isotropic shf interaction is attributed to admixture of the unoccupied ligand-cation 4s orbital into the outer d orbital of the central impurity ion. The anisotropic contribution to the shf interaction is attributed to admixture of 4p ligand-cation orbitals. The results suggest an increase in the probability of delocalization of the unpaired spin onto the nearest-neighbor cations as n increases, however, for the Nb impurity, the degree of delocalization is found to be anomalously high. Extension of this type of analysis to treatment of these impurities in the isomorphs TiO2 and SnO2 is discussed.

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