The Mn6+ ion is a promising activator ion for tunable and short-pulse laser materials because of its broadband luminescence in the spectral region 850-1600 nm and its simple 3d1 electronic configuration, which excludes an occurrence of undesirable exited-state absorption into higher 3d levels. However, hexavalent manganese can be stabilized only in the tetrahedral oxo-coordination and easily reduces to Mn5+ or Mn4+ at temperatures above 600°C. Recently, flux  and liquid-phase epitaxy (LPE)  growth of Mn6+-doped sulfates has been reported, while except for BaMoO4:Mn6+  investigations on the mechanically more stable alkaline-earth-metal molybdates and tungstates as possible host materials for efficient Mn6+ incorporation have as yet not been reported. We investigated the growth conditions of undoped and Mn6+-doped MAO4, with M = Ca, Sr, Ba and A = S, Mo, W, from the ternary NaCl-KCl-CsCl solvent at temperatures 480-600°C. The growth rates increase in the series tungstates < molybdates < sulfates and depending on the cation, in the series Ca < Sr < Ba. The dopant ion Mn6+ can be easily incorporated into BaSO4, less well into BaMoO4 and BaWO4, whereas for Ca- and Sr-containing tungstates and molybdates no significant doping was found, independent on the concentration of Mn6+ in the liquid solution. Moreover, reduction of the Mn6+ ion cannot be avoided, even at the presence of oxidizing additives such as K2CO3 or NaOH. LPE was employed for growing Mn6+-doped layers of BaAO4 compounds. Growth velocities of 3-5 µm/h in the temperature interval from 490-540°C from chloridic solution, containing 0.3-1mol% of K2MnO4 with respect to the solute, delivered dark-pink BaSO4 and slightly green BaMoO4 and BaWO4 layers up to 200 µm in thickness. With respect to high Mn6+ doping levels, BaSO4 is the most suitable host material and its further investigation under different initial concentrations of manganese is currently underway.  T.C. Brunold, H.U. Güdel, Inorg. Chem. 36, 1946 (1997).  D. Ehrentraut, M. Pollnau, Appl. Phys. B 75, 59 (2002).  T.C. Brunold, H.U. Güdel, Chem. Phys. Lett. 249, 77 (1996).
|Number of pages||1|
|Publication status||Published - Jul 2003|
- IOMS-APD: Active Photonic Devices