EPR and optical properties of KY(W0 4 ) 2 :Gd 3+ powders
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Lucyna Macalik
Institute of Low Temperature and Structure Research, PAS, 50-950 Wrocł aw, Poland
Sławomir Maksymilian Kaczmarek and Tomasz Skibinski West Pomeranian University of Technology, Faculty of Mechanical Engineering and Mechatronics, Institute of Physics, 70-310 Szczecin, Poland
Jerzy Hanuza
Institute of Low Temperature and Structure Research, PAS, 50-950 Wrocł aw, Poland (Received 28 March 2012; accepted 6 September 2012)
Comparisons of structural, optical, and magnetic properties between KY(WO4)2 (KYW) powders doped with Gd31 from 0.5 up to 100 mol% and KGd(WO4)2 and KYW single crystals have been made. For this purpose, x-ray diffraction (XRD), infrared (IR), Raman, and electron paramagnetic resonance (EPR) spectra were collected. The XRD studies have verified the quality of the synthesis of compounds and have shown the differences in the positions of the diffraction peaks due to the change in concentration of gadolinium ions. Raman and IR spectra confirmed that the phases are isostructural. The optimization of the spin Hamiltonian parameters and EPR data simulation was achieved by using the electron paramagnetic resonance and nuclear magnetic resonance (EPR-NMR) program. Changes in kind of magnetic interactions were found and analyzed from the point of view of their dependence of the compound form (powder, single crystal), temperature, and gadolinium ion concentration. The investigated compounds revealed complex interactions between gadolinium ions both in a type and a strength. I. INTRODUCTION
Double tungstates containing rare-earth ions are attractive laser host materials due to very high stability of emission, high efficiency, long lifetime, and low excitation threshold as well as excellent chemical and thermal durability in air. This group of crystals is good candidate for efficient stimulated Raman scattering as well as for fabrication of high efficiency lasers with high output energy.1 They create a family of compounds with general formula AIREIII(WVIO4)2 where A denotes an alkali metal ion and RE denotes a rare-earth ion. These compounds crystallize in the structure, whose prototype is the scheelite- or wolframite-type structure. RE31 and A1 ions can be coordinated by oxygen ions and have 8 and 12 coordinated number, respectively. Rare-earth oxygen polyhedra form square antiprism units, while the alkali metal polyhedra form distorted icosahedron units. In dependence of kind of alkali metal, tungsten atoms build isolated WO4 tetrahedra or deformed WO6 octahedra connected by a common edge forming double chains of W2O10.2–6 The KY(WO4)2 (KYW) and KGd(WO4)2 (KGW) tungstates crystallize in the monoclinic structure C2/c 5 C2h6 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.345 J. Mater. Res., Vol. 27, No. 23, Dec 14, 2012
http://journals.cambridge.org
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with Z 5 4.4,7 In this structure, the tungstate units built the WO6 octahedra joined through the single and double oxygen bridges. The RE31 ions occupy the sites of C1 and C2 sy
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