Abstract
X-ray diffraction, neutron diffraction, optical and absorption spectroscopy, electron probe microanalysis, and temperature-dependent electrical conductivity measurements were used to study structural features and defect generation to be responsible for coloring of single crystals of nominal compositions (Na0.5LaxGd0.5 − x)MoO4:Tm having scheelite structure which were Czochralski grown under a weakly oxidizing atmosphere followed by air annealing. In nonannealed crystals, the color was found to be due to oxygen vacancies and their compensator electrons (black color) and, most likely, electrons located on Mo6+ ions (lilac color); the concentration of these defects decreased upon air annealing, thereby discoloring the samples. The yellow color of crystals was interpreted as arising from possible formation of a color center (an association of a molybdenum vacancy and a hole).
Published Version
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