X-ray Diffraction Study of the Structure and Defect System of Yb-Activated (Na_(0.5)Gd_(0.5))WO_4 Crystals

摘要

Nominally pure and Yb-activated Czochralski-grown (Na_(0.5)Gd_(0.5))WO_4 crystals (scheelite type) were studied by x-ray diffraction (phase analysis, unit-cell parameters, and structure refinement by the Rietveld method and single-crystal techniques). A pseudotetragonal (orthorhombic) superstructure was revealed, which was shown to have doubled unit-cell parameters compared to the scheelite cell. Some of the crystals were found to contain tungsten and oxygen vacancies, which give rise to additional optical absorption. The effects of the growth and heat-treatment conditions and Yb activation on the structure, defect system, and additional absorption spectrum of (Na_(0.5)Gd_(0.5))WO_4 are analyzed.