[en] Nd:Gd₃Ga₅O₁₂ crystals with different concentrations of Nd³⁺ were grown by Czochralski method, their absorption spectra were measured at room temperature. By using the optical absorption method, the effective distribution coefficient k_eff for Nd³⁺ in GGG was fitted to be 0.40±0.01, which is higher than that of Nd³⁺ in YAG. The 808nm absorption cross-section was calculated to be 4.0±0.2 x 10^-20 cm^-2. The lengthways and radial concentration distribution of Nd³⁺ in the crystals were also analyzed and discussed. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Spectroscopic ellipsometry was used to study the dielectric function of a hole-doped Ba_0.68K_0.32Fe₂As₂, with a sharp (ΔT<0.6 K) transition to the SC state below T_c∼38.5 K, in the spectral range 0.012-6.5 eV at temperatures 7-300 K. The optical conductivity spectra are dominated by a series of interband transitions, which all agree well with the predictions of LDA calculations. Our results provide clear evidence of SC gap formation in the far-infrared optical conductivity spectra, 2Δ_SC∼5.5-6.5 k_BT_c. We find the penetration depth to be 1600 A in close agreement with the values determined by other techniques. The data also provide detailed information about the evolution of the optical self-energy in the normal and SC states. The frequency and temperature dependencies of the SC gap formation speak for the extended s_±-wave pairing symmetry with strong coupling to the intermediate boson mode centered at ∼25 meV. Examination of the conductivity in the optical spectral range uncovered superconductivity-induced suppression of interband transitions at energies more than 200Δ_SC.

[en] A large oxypnictides family LnFeAsO (Ln=La,Ce, Pr,Nd,Sm,Gd) has been found to be superconducting with a transition temperature up to 55 K and high upper critical fields. The onset of the superconducting critical temperature T_c in these compounds increases with the reduction of the rare-earth ionic size, and the highest T_c obtained so far is 55 K in doped SmFeAsO. In this contribution we present results of X-ray absorption (XAS) spectroscopy measurements on the soft X-ray regime for polycrystalline LaFeAsO, CeFeAsO, SmFeAsO and GdFeAsO at various temperature as well as for Ba_1-xK_xFe₂As₂ single crystals.

[en] The 1.5 at.% Er³⁺ doped gadolinium scandium gallium garnet (GSGG) laser crystal with high optical quality was successfully grown by the Czochralski method. The structural parameters were obtained by x-ray Rietveld refinement. A high crystalline quality of Er:GSGG was determined by x-ray rocking curve. The spectroscopic parameters of Er³⁺ ion were calculated and analyzed using the Judd–Ofelt theory. Furthermore, the stimulated-emission cross-section spectra were investigated for the ⁴I_13/2  →  ⁴I_15/2 transitions at 1.5–1.6 µ m, which indicates the great potential of Er:GSGG for multi-wavelength emission at 1.5–1.6 µ m. The larger emission cross-section and long fluorescence lifetimes around 0.55 and 0.67 µ m mean that the 1.5 at.% Er:GSGG crystal is beneficial for green and red laser generation. Meanwhile, the intensity of the emission spectra was compared between the 1.5 at.% and 2.0 at.% Er-doped GSGG. The roles of cross-upconversion, cross-relaxation and the excited-state absorption process were discussed in the 1.5 at.% Er:GSGG crystal for generating visible and 1.5–1.6 µ m lasers. (paper)

[en] Highlights: • A new yellow laser crystal Dy³⁺ doped GdScO₃ was grown successfully by Cz method. • The transition intensity parameters Ω_t are first obtained by J-O theory. • Dy:GdScO₃ has larger σ_α than Dy:YAG crystal and the FWHM at 453 nm is 9 nm. • Dy:GdScO₃ exhibits relatively long τ_f of 459 μs and high η of 70.6%. - Abstract: High-quality Dy³⁺ doped GdScO₃ (Dy:GdScO₃) single crystal was grown successfully by the Czochralski method for the first time. The lattice parameters of the as-grown crystal were obtained by Rietveld refinement to its XRD patterns. The effective segregation coefficient of Dy³⁺ is calculated to be 0.68. The spectroscopic characteristics of Dy:GdScO₃ are investigated, with special attention to the yellow emission that could be pumped directly by the rapidly developed blue GaN LD. The absorption cross section of Dy:GdScO₃ at 453 nm is 1.8 × 10^-21 cm² and the FWHM of this absorption band is about 9 nm at 300 K. Meanwhile, Dy:GdScO₃ exhibits strong yellow emission at 577 nm corresponding to the transition ⁴F_9/2→⁶H_13/2 with stimulated emission cross section of 4.1 × 10^-21 cm². The relatively long fluorescence lifetime (459 μs) and high radiative quantum efficiency of the ⁴F_9/2 level indicate a high laser efficiency of Dy:GdScO₃ crystal. All results suggest that Dy:GdScO₃ crystal could be a promising candidate for yellow laser at 577 nm pumped by blue GaN LD.

[en] In superconducting thin films as well as in non-ideal single crystals the distribution of magnetic flux quanta is affected by existing defects. This interplay between repulsive vortex-vortex interaction and attractive pinning ends up in a strongly disordered vortex arrangement. Visualization of flux lines with magnetic force microscopy (MFM) followed by the quantitative analysis of data offers direct insight into pinning mechanism on a local scale. We have performed quantitative analysis of MFM images of two superconductors: single crystalline BaFe_2-xCo_xAs₂ and NbN thin films. Statistical evaluation of the images allows us to conclude about the existence of a short range hexagonal order in the FeAs crystal with strong pinning sites. Evaluation of the measured signal in NbN thin films gives us an information about the local pinning force as well as the magnetic penetration depth.

[en] The Judd–Ofelt theoretic transition intensity parameters of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence. It is very difficult to determine them with emission or absorption spectra for a long time. A “full profile fitting” method to obtain in solids with its emission spectrum is proposed, in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability, line profile function, instrument measurement constant and transition center frequency or wavelength, and the whole experimental emission spectrum is the sum of all transitions. In this way, the emission spectrum is expressed as a function with the independent variables intensity parameters , full width at half maximum (FWHM) of profile functions, instrument measurement constant, wavelength, and the Huang–Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered. The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting and other parameters. Employing this method obviates measurement of the absolute emission spectrum intensity. It also eliminates dependence upon the number of emission transition peaks. Every experiment point in emission spectra, which usually have at least hundreds of data points, is the function with variables and other parameters, so it is usually viable to determine and other parameters using a large number of experimental values. We applied this method to determine twenty-five of Yb³⁺ in GdTaO₄. The calculated and experiment energy lifetimes, experimental and calculated emission spectrum are very consistent, indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions’ emission spectrum. The calculated emission cross sections of Yb³⁺:GdTaO₄ also indicate that the F–L formula gives larger values in the wavelength range with reabsorption. (paper)

[en] A novel mixed laser crystal of Nd:GdLaNbO₄ (Nd:GLNO) was grown successfully by conventional Czochralski method. The unit cell parameters were obtained by Rietveld refinement method. The density of the as-grown crystal was measured by Archimedean buoyancy method and calculated in theory. Absorption spectrum of Nd:GLNO crystal was recorded at room temperature, and 11 absorption peaks were assigned. The defects of Nd:GLNO crystal were revealed by using chemical etching method with phosphoric acid as etchant. The mechanical properties (including hardness, yield strength, elastic stiffness constant, fracture toughness and brittleness index) were systemically estimated based on Vickers hardness test. All these obtained results play a quite important role in further investigation of Nd:GLNO crystal. (orig.)

[en] Using low temperature magnetic force microscopy (MFM) we imaged the vortex distribution in a slightly overdoped BaFe_2-xCo_xAs₂ (x=0.19, T_c=23 K) superconducting single crystal. Our local method reveals that at low fields (3 mT und 6 mT) the superconducting flux lines arrange in a vortex glass phase with only a short-range order. This denotes a presence of pinning centres which prohibit a formation of the ordered Abrikosov lattice. From the statistical processing of MFM data we have extracted the radial correlation length ζ of the vortex lattice and have established the hexagonal local lattice symmetry. It reveals that the visualized vortex distribution can be treated as a disordered triangular lattice. Moreover, the isothermal magnetization loops measured at various temperatures in a wide field range up to 14 T exhibit the ''fishtail'' effect that is known to be related to the vortex pinning and to the crossover between two different regimes of the vortex lattice.

[en] A Nd-doped GdNbO_4 crystal was grown successfully by Czochralski method. Its monoclinic structure was determined by X-ray diffraction; the unit-cell parameters are a = 5.38 Aa, b = 11.09 Aa, c = 5.11 Aa, and β = 94.56 . The morphological defects of Nd:GdNbO_4 crystal were investigated using the chemical etching with the phosphoric acid etchant. For a new crystal, the physical properties are of great importance. The hardness and density of Nd:GdNbO_4 were investigated first. Thermal properties of Nd:GdNbO_4, including thermal expansion coefficient and specific heat, were measured along a-, b-, and c-crystalline axes. Thermal properties indicate that the Nd:GdNbO_4 pumped along c-axis can reduce the thermal lensing effect effectively. The specific heat is 0.53 J g"-"1 K"-"1 at 300 K, indicating a relatively high damage threshold of Nd:GdNbO_4. The transmission and emission spectrum of Nd:GdNbO_4 were measured, and the absorption peaks were assigned. The strongest emission peak of Nd:GdNbO_4 is located at 1065.3 nm in the spectral range of 850-1420 nm excited by 808 nm laser. The refractive index of Nd:GdNbO_4 was calculated with the transmission spectrum and fitted with Sellmeier equation. All these obtained results is of great significance for the further research of Nd:GdNbO_4. (orig.)