Structural, electronic and optical properties of BaRE6(Ge2O7)2(Ge3O10) (RE = Tm, Yb, Lu) compounds and BaYb6(Ge2O7)2(Ge3O10):Tm3+ and BaLu6(Ge2O7)2(Ge3O10):Yb3+,Tm3+ phosphors: potential applications in temperature sensing.

A new series of BaRE6(Ge2O7)2(Ge3O10) (RE = Tm, Yb, Lu) germanates and activated phases BaYb6(Ge2O7)2(Ge3O10):xTm3+ and BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ have been prepared using a solid-state reaction. An XRPD study has revealed that the compounds crystallize in the monoclinic system (space group P21/m, Z = 2). The crystal lattice consists of zigzag chains of edge-sharing distorted REO6 octahedra, bowed trigermanate [Ge3O10] units, [Ge2O7] groups, and eight-coordinated Ba atoms. The density functional theory calculations have confirmed a high thermodynamic stability of the synthesized solid solutions. According to the results of vibrational spectroscopy studies and diffuse reflectance measurements, the BaRE6(Ge2O7)2(Ge3O10) germanates are promising compounds for the creation of efficient lanthanide ion activated phosphors. Under 980 nm laser diode excitation, the BaYb6(Ge2O7)2(Ge3O10):xTm3+ and BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ samples exhibit upconversion luminescence corresponding to the characteristic 1G4 → 3H6 (455-500 nm), 1G4 → 3F4 (645-673 nm) and 3H4 → 3H6 (750-850 nm) transitions in Tm3+ ions. Heating of the BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ phosphor with the optimal composition up to 498 K leads to the enhancement of a broad band at 673-730 nm, caused by 3F2,3 → 3H6 transitions. It has been revealed that the fluorescence intensity ratio between this band and the band at 750-850 nm may be used for temperature sensing. The absolute and relative sensitivities in the studied temperature range reach 0.021% K-1 and 1.94% K-1, respectively.

Coagulation removal of nickel (II) ions by ferric chloride: Efficiency and mechanism.

Removal of heavy metal ions, in particular, divalent nickel ions from natural and wastewater, is of great importance for the environment. Nickel (II) ions are very toxic and provoke many diseases. The purpose of this work was to study the possibility of removing toxic nickel (II) ions from polluted water using an iron (III) chloride (FeCl3) coagulant. It is shown that the removal of nickel ions from aqueous solution by iron (III) hydroxide precipitate formed during the coagulation process at pH 7 and 8 is described with satisfactory accuracy by the classical adsorption isotherms of Freundlich, Langmuir, and Dubinin-Radushkevich. The studies performed with the use of X-ray powder diffraction and thermal analyses, IR, Raman, and Mössbauer spectroscopy have shown that the uptake of nickel ions by iron (III) hydroxide precipitate is due to simple physical adsorption and is not accompanied by the formation of mixed iron and nickel compounds. No alloying of the formed iron (III) hydroxide precipitate with nickel ions takes place either. The formed iron (III) hydroxide precipitate is a two-line ferrihydrite having the gross formula Fe2 O3 × 3H2 O. Its sorption capacity for nickel ions is almost an order of magnitude higher than that of some mineral and carbon sorbents, and at pH 7 and 8, it is 60.5 and 141.9 mg/g, respectively. PRACTITIONER POINTS: Coagulant FeCl3 cleans contaminated solutions from Ni(II) ions. Iron (III) hydroxide precipitated at pH 7 and 8 is a two-line ferrihydrite Fe2 O3  × 3H2 O. Removing of Ni(II) ions is described by classical adsorption isotherms. The most complete removal of Ni(II) ions occurs at pH = 8.

Synthesis and characterisation of new MO(OH)2 (M = Zr, Hf) oxyhydroxides and related Li2MO3 salts.

Two new solid MO(OH)2 (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P2(1)/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling.