Flux growth and liquid phase epitaxy of undoped and Mn6+-doped sulfates, tungstates, and molybdates

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 [1] and liquid-phase epitaxy (LPE) [2] growth of Mn6+-doped sulfates has been reported, while except for BaMoO4:Mn6+ [3] 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.\ud 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.\ud 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.\ud \ud [1] T.C. Brunold, H.U. Güdel, Inorg. Chem. 36, 1946 (1997).\ud [2] D. Ehrentraut, M. Pollnau, Appl. Phys. B 75, 59 (2002).\ud [3] T.C. Brunold, H.U. Güdel, Chem. Phys. Lett. 249, 77 (1996)

Liquid phase epitaxy and optical investigation of KYb(WO4)2 thin layers

In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm [1], which provides high efficiency and reduced heat generation. Of high practical interest is the thin-disk laser concept [2], which possesses a tremendous advantage over rod lasers because of its axial-cooling approach and consequent weak thermal lensing and good beam quality.\ud A promising material for Yb3+ thin-disk lasers is KYb(WO4)2 (KYbW) [3]. It can be grown from high-temperature solutions [4]. Nevertheless, the growth of high-quality, single-crystalline layers with thickness in the range of the absorption length of ~13 µm at 981 nm has as yet not been reported. A suitable substrate material is KY(WO4)2 (KYW), but the relatively large differences in the thermal expansion coefficients between KYW and KYbW along the [100], [001], and especially [010] directions [5] favor low temperatures for the hetero-epitaxial growth.\ud For the first time, we demonstrate liquid phase epitaxy (LPE) of KYbW layers. The layers were grown at start temperatures as low as 520°C, which is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. KY1-xYbx(WO4)2 layers with varying x = 0.03-1.00 were grown by LPE. The chloride solvent consisted of the eutectic composition [6] 24.4 mol.% KCl, 30.4 mol.% NaCl, and 42.2 mol.% CsCl. The growth temperature spanned the range from 580 to 500°C and the cooling rate was 0.67-1.00 Kh-1. Crack-free, transparent KYbW layers were grown on (010) substrates.\ud Spectroscopic investigations have shown that the lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [4]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud \ud [1] T.Y. Fan, IEEE J. Quantum Electron. 29, 1457 (1993).\ud [2] A. Giesen, H. Hügel, A. Voss, K. Wittig, U. Brauch, H. Opower, Appl. Phys. B 58, 365 (1994).\ud [3] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 74, 185 (2002).\ud [4] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 65, 165121 (2002).\ud [5] M.C. Pujol, X. Mateos, R. Solé, J. Massons, J. Gavaldà, F. Díaz, M. Aguiló, Mater. Sci. Forum 378-381, 710 (2001).\ud [6] D. Ehrentraut, M. Pollnau, S. Kück, Appl. Phys. B 75, 59 (2002)

Liquid phase epitaxy and spectroscopic investigation of optically active KYb(WO4)2 thin layers

In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 µm, which provides high efficiency and reduced heat generation. A promising material for Yb3+ lasers is KYb(WO4)2 (KYbW) [1]. It can be grown from high-temperature solutions [2]. A suitable substrate material for the growth of single-crystalline layers with thicknesses in the range of the absorption length of ~13 µm at 981 nm is KY(WO4)2 (KYW).\ud We demonstrate the liquid phase epitaxy (LPE) of KYbW layers at start temperatures as low as 520°C from the chloride solvent KCl-NaCl-CsCl. This temperature is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented KYW substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. Our spectroscopic investigations show that the fluorescence lifetime of ~250 µs measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [2]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud \ud [1] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. Solé, J. Gavaldà, M. Aguiló, F. Güell, J. Massons, T. Kirilov, F. Díaz, Appl. Phys. B 2002, 74, 185\ud [2] M.C. Pujol, M.A. Bursukova, F. Güell, X. Mateos, R. Solé, J. Gavaldà, M. Aguiló, J. Massons, F. Díaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 2002, 65, 16512

Cyber security and data privacy

The importance of cyber security and data privacy is described in the paper. Common threats to computer systems and ways how to minimise risks are mentioned. Worldwide Data Privacy Regulations are presented

The variation of the magnetic field of the Ap star HD~50169 over its 29 year rotation period

Context. The Ap stars that rotate extremely slowly, with periods of decades to centuries, represent one of the keys to the understanding of the processes leading to the differentiation of stellar rotation. Aims. We characterise the variations of the magnetic field of the Ap star HD 50169 and derive constraints about its structure. Methods. We combine published measurements of the mean longitudinal field of HD 50169 with new determinations of this field moment from circular spectropolarimetry obtained at the 6-m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Sciences. For the mean magnetic field modulus , literature data are complemented by the analysis of ESO spectra, both newly acquired and from the archive. Radial velocities are also obtained from these spectra. Results. We present the first determination of the rotation period of HD 50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap star for which magnetic field measurements have been obtained over more than a full cycle. The variation curves of both and have a significant degree of anharmonicity, and there is a definite phase shift between their respective extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its orbital elements, and suggest that the secondary is probably a dwarf star of spectral type M. Conclusions. The shapes and mutual phase shifts of the derived magnetic variation curves unquestionably indicate that the magnetic field of HD 50169 is not symmetric about an axis passing through its centre. Overall, HD 50169 appears similar to the bulk of the long-period Ap stars.Comment: 10 pages, 3 figures, accepted for publication in A&

Low-temperature flux growth of sulfates, molybdates, and tungstates of Ca, Sr, and Ba and investigation of doping with Mn 6 +

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 performe

PROCEDURE OF DETERMINING SCALAR PRODUCT OF TWO VECTORS GIVEN IN POLAR COORDINATES FOR THE TASKS OF COMPUTER GRAPHICS

Запропоновано нову формулу для визначення скалярного добутку двох векторів, заданих у полярних координатах, яка дозволяє зменшити обчислювальні витрати та прискорити процес формування реалістичних зображень. Запропоновано структурну схему блока визначення скалярного добутку двох векторів, у якому реалізовано нову формулу.There had been proposed new formula for determining the scalar product of two vectors given in polar coordinates, which reduces the computational cost and accelerate the formation of realistic images. There had been proposed a block diagram of unit for definition of scalar product of two vectors, in which new formula was implemented