Amorphous anodic oxide films on InAlP have been grown at high efficiency in sodium tungstate electrolyte. The films are shown to comprise an outer layer containing indium species, an intermediate layer containing indium and aluminium species and an inner layer containing indium, aluminium and phosphorus species_. The layering correlates with the influence on cation migration rates of the energies of In³⁺–O, Al³⁺–O and P⁵⁺–O bonds, which increase in this order. The film surface becomes increasingly rough with increase of the anodizing voltage as pores develop in the film, which appear to be associated with generation of oxygen gas.

 

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Fluorescence, excitation, and pulsed fluorescence measurements have been made on a single crystal of CaWO₄ over a wide temperature range. The temperature dependences of the integrated fluorescence intensities and lifetimes were obtained for different excitation wavelengths. A sharp increase in the fluorescence lifetimes is observed below about 75°K and zero‐phonon lines can be observed. These results are used to formulate a model for the tungstate luminescent center based on the ion in a crystal field of S ₄ symmetry. Energy migration and impurity trapping effects are also discussed.

 

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Due to unknown effects of the potential exposure of the terrestrial environment to tungsten substances, a series of toxicity studies of sodium tungstate (Na₂WO₄) was conducted. The effect on earthworm (Eisenia fetida) survival and reproduction was examined using Organisation for Economic Co-operation and Development (OECD) Guideline 222. No effect on either endpoint was seen at the highest concentration tested, resulting in a 56-d no-observed-effect concentration (NOEC) of ≥586 mg tungsten/kg dry soil (nominal concentrations). The effect of sodium tungstate on emergence and growth of plant species was examined according to OECD Guideline 208: oat (Avena sativa), radish (Raphanus sativus), and lettuce (Lactuca sativa). No effects on emergence, shoot height, and dry shoot weight were observed in oats exposed to the highest concentration, resulting in a 21-d NOEC of ≥586 mg tungsten/kg dry soil. The NOECs for radish and lettuce were 65 and 21.7 mg tungsten/kg dry soil (nominal concentrations), respectively. Respective 21-d median effective concentration values (EC50) for radish and lettuce were >586 and 313 mg tungsten/kg dry soil (based on shoot height) (confidence level [CL] -8.5-615); EC25 values were 152 (CL 0-331) and 55 (CL 0-114) mg tungsten/kg dry soil. Results are consistent with the few other tungsten substance terrestrial toxicity studies in the literature.

 

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The influence of annealing in different atmospheres on absorption and luminescent properties of high-quality undoped CaWO₄ single crystals is presented. The decreasing of green emission intensity after annealing in oxygen and air have been revealed, while two well-defined maxima near 25,000 and 32,000cm^-1 can be observed in the induced absorption spectra. These maxima are attributed to the interstitial oxygen, possibly in the form of the O⁻-centre. The increase of the blue/green luminescence ratio has been revealed after annealing in nitrogen while the crystal transparency remains unaffected. The possible ways to reduce slow green emission component without changing crystal absorption are shown. Structure of colour centres and the models of revealed processes are discussed.

 

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