Electron spin resonance (ESR) and infrared absorption (IR) experiments have provided information about the role of aluminum in the radiation response of commercially available high-quality synthetic quartz. Samples obtained from two separate sources were investigated, and identical radiation responses were found for the two materials. Interstitial ions such as H+, Li+, and Na+ as well as radiation-induced holes trapped at oxygen ions act as charge compensators for the ever-present substitutional aluminum ions. Usually the charge compensator is located adjacent to the aluminum, and this gives rise to Al-OH−, Al-Li+, Al-Na+, and [Ale+]0 centers. Absolute concentrations of these compensated aluminum centers have been determined as a function of irradiation and annealing temperature for a variety of samples, both swept and unswept. The various treatments simply exchange one type of compensator for another at the aluminum sites, and within experimental error, the sum of the aluminum centers remains constant for a given sample. This direct accountability of all the aluminum ions in hydrogen-swept samples strongly suggests that the 3306- and 3367-cm−1 infrared bands are associated with the Al-OH− center. Also, the ESR and IR results show that the aluminum content of randomly selected bars of high-quality quartz can vary by an order of magnitude.

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Doping the photorefractive material bismuth germanium oxide Bi12GeO20(BGO) with chromium significantly affects its optical properties. An absorption spectrum taken at 300 K shows that the introduction of chromium produces a strong unresolved band which overlaps the absorption cutoff of BGO and a series of smaller overlapping bands between 650 and 1100 nm. Cooling BGO:Cr to 10 K sharpens the small bands and resolves the strong band into a peak near 510 nm. This peak is responsible for the reddish-brown color of BGO:Cr. Excitation at room temperature with visible light increases the bands in the 650–1100 nm range. The production of this additional room temperature photochromic absorption is most efficient with excitation near 490 nm but extends throughout the visible. Chromium occupies the tetrahedral germanium site in BGO; and the observed spectra are consistent with a Cr4+ tetrahedral state. During crystal growth some of the chromium gives up an electron to the antisite bismuth native defect and becomes Cr5+. Exposing the sample to light returns the electron to the chromium and increases the Cr4+ absorption. The photoinduced absorption is thermally stable for temperatures up to about 425 K. This stability suggests that doping BGO with Cr should lead to room temperature persistent photorefractive gratings. © 2001 American Institute of Physics.

The thermal conductivities of three large single crystals of zinc oxide have been measured, two from 3.5 to 300 K and one from 1.1 to 300 K. Two of the samples were hydrothermally grown and lithium doped, and one sample was vapor grown and undoped. The heat flow was parallel to the c‐axis of one lithium‐doped crystal and of the vapor grown crystal. These c‐axis crystals had room temperature electrical resistivities of 0.4 and 5.0 Ωcm respectively. The heat flow was parallel to the a‐axis in the other crystal, which had a room temperature electrical resistivity of approximately 106 Ωem as a result of the lithium doping. A very small anisotropy in the thermal conductivity was measured and is consistent with the results which are predicted from the Steigmeier and Kudman relation. The data were analyzed in terms of the Debye‐Callaway model with a relaxation time that included boundary, dislocation, point defect, and Phonon–phonon scattering.

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