The crystal structure of monoclinic KLu(WO 4 ) 2 (KLuW) crystals was determined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters were a = 10.576 (7), b = 10.214 (7), c = 7.487 (2) Å , = 130.68 (4) , with Z = 4, in space group C2/c. The unit-cell parameters of KLu 1Àx Yb x (WO 4 ) 2 were determined in relation to Yb concentration. Vickers micro-indentations were used to study the microhardness of KLuW. The linear thermal expansion tensor was determined and the principal axis with maximum thermal expansion ( 0 33 = 16.72 Â 10 À6 K À1 ), X 0 3 , was located 13.51 from the c axis. The room-temperature optical tensor was studied in the near-infrared (NIR) and visible range. The principal optical axis with maximum refractive index (n g = 2.113), N g , was located 18.5 from the c axis at 632.8 nm. Undoped and ytterbium-doped KLuW crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, { " 1 111}, {010} and {310} faces that basically constitue the habit of the KLuW crystals.

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Epitaxial monoclinic double tungstate laser crystals were grown with high crystalline quality. Based on these Yb-doped composites, laser operation was demonstrated. Continuous-wave laser emission of a Yb:KYW∕KYW crystal was achieved at 1030nm. The 25-μm-thin Yb:KYW layer was pumped at wavelengths near 980nm by a Ti:sapphire laser. A maximum output power of 40mW was obtained at room temperature.

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Epitaxial layers of KLu 1-x Yb x (WO 4 ) 2 /KLu(WO 4 ) 2 with different Yb concentrations were grown by liquid-phase epitaxy. The quality of the epitaxial layers principally depends on the Yb concentration and the crystal face. In solutions with up to 50 mol % of substitution of Lu 2 O 3 by Yb 2 O 3 , defect-free layers can be grown and the highest quality face is (010). The layers grown on the (-111) face tend to have a higher density of morphologies. The optical spectroscopy of Yb 3+ in thin layers coincides with that obtained in doped bulk crystals.

We successfully grew langbeinite-type structures containing Ti4+ and Ln3+ ions as M2Ti2 - x Ln x (PO4)3 crystals (M = K+ or Rb+ and Ln = Er3+ or Yb3+) by high-temperature-solution methods. We took accurate composition measurements of these crystals, paying special attention to the lanthanide contents. We resolved the structure of the Rb2Ti1.01Er0.99(PO4)3 crystal and studied the evolution of this structure with the temperature. We found that this compound decomposed at 1323 K. We made a preliminary study to check the nonlinear optical properties of these materials, showing that the second-harmonic generation efficiency of the Rb2Ti1.01Er0.99(PO4)3 was at least similar to that of potassium dihydrogen phosphate.

As revealed by single crystal XRD, the violet title compound crystallizes in the cubic space group P2 1 3 with Z = 4. Preliminary measurements show that the second-harmonic generation efficiency of the title compound is at least similar to that of KH 2 PO 4 . The crystals may be used as laser and self-doubling materials. -(CARVAJAL, J. J.; AZNAR, A.; SOLE, R.; GAVALDA, J.; MASSONS, J.; SOLANS, X.; AGUILO, M.; DIAZ*, F.; Chem. Mater. 15 (2003) 1, 204-211; Fis. Cristallogr. Mater., Univ. Rovira Virgili, E-43005 Tarragona, Spain; Eng.) -W. Pewestorf 12-009

Monoclinic layers of KY1−xYbx(WO4)2 with a thickness of up to 330 µm were grown on KY (WO4)2 substrates by liquid phase epitaxy (LPE) using K2W2O7 solvent. The layers grown from solutions of up to 7.5 at.% substitution of Y by Yb generally had flat surfaces on {010} and {110} crystal faces with no macroscopic defects at the layer/substrate interface. Already at 10 at.% of Yb substituting Y, some defects at the interface tend to appear and increase for higher concentrations. The layers grown on {310} and faces show more growth instabilities even at low Yb concentrations. The thermal evolutions of the lattice mismatches between the epilayer and the substrate for {010}, {110}, {310} and faces were calculated to range from 0.55% at 1273 K to −0.31% at 298 K. The optical spectroscopic studies carried out with these samples agree well with Yb-doped KYW bulk crystals, the measured absorption and calculated (by the reciprocity method) emission cross-sections at 981 nm with being σabs = 12.5 × 10−20 cm2 and σem = 15.8 × 10−20 cm2, respectively.