Low-temperature flux growth of sulfates, molybdates, and tungstates of Ca, Sr, and Ba and investigation of doping with Mn6+

The growth of undoped and Mn6+-doped molybdates and tungstates of alkali-earth metals and BaSO4 has been investigated. Single crystals were grown by the flux method within the temperature range of 600-475 C, using the ternary NaCl-KCl-CsCl solvent. Sizes of undoped crystals increase within the series tungstates<molybdates<sulfate and, depending on the cation, within the series Ca2+∝Sr2+<Ba2+. The Mn6+ ion tends to be reduced to Mn5+/Mn4+ with time in the chloride solution, but can be partly stabilized by the addition of alkali-metal carbonates or hydroxides. The incorporation of Mn6+ is governed by the coordination of the MnO4-2 tetrahedron in the crystal. No significant doping was found for Ca and Sr compounds and only small amounts of Mn6+ were incorporated into BaMoO4 and BaWO4. Crystals with orthorhombic space group Pnma such as BaSO4 exhibit significantly higher doping levels. The Mn6+ distribution in each crystal varies due to manganese reduction with growth time. Temperature-, time-, and concentration-dependent spectroscopy of BaSO4:Mn6+ was performed