The reflectivity spectra of Cd_{1-x}Mn_{x}F_{2} crystals, in the 5-35 eV energy range at 300 and 77 K, were investigated. The observed changes in the shape of spectra, caused by increase of the Mn content, are compared with the calculated band structure of pure CdF_{2} and with the already available results of XPS experiments for these crystals. The increasing concentration of Mn results in the blurring of the reflectivity structures and shifts the energy of direct exciton (as compared to pure CdF_{2}). Qualitative arguments (hybridization of Mn^{2+} 3d and F^{-} 2p states) can describe these effects but a quantitative explanation would require a detailed band structure calculation for these compounds.
This paper presents the results of investigations of the radiation effects in NH_2(CH_3)_2Al(SO_4)_2×6H_2O crystals doped with chromium. On the basis of absorption spectroscopy and resonance Raman scattering study it has been shown that comparatively low doses of radiation first of all causes recharging of Cr^{3+} on Cr^{4+} ions. Besides, the processes of dehydrogenation and the changes in arrangement of the hydrogen bond network were observed. These changes are followed by distortion of the complexes bonded by such a type of bonds.
The optical band positions and the spin-Hamiltonian parameters (g factors g_{∥}, g_{⊥}, and zero-field splitting parameter D) of alum α-RbAl(SO₄)₂·12H₂O:Cr³⁺ are calculated by diagonalizing the 120× 120 complete energy matrix based on the two-spin-orbit-coupling-parameter model. The model takes into account not only the contributions due to the spin-orbit-coupling parameter of central d^{n} ion in the conventional crystal field theory, but also those due to ligands via covalence effect. The calculation indicates that the fourteen observed spectral data (eleven optical band positions and three spin-Hamiltonian parameters) can be reasonably and uniformly explained with four adjustable parameters (the Racah parameters B, C, intrinsic parameter A̅₄(R) in the superposition model, and the trigonal distortion angle β). The calculations also suggest that contrary to the previous findings, the trigonal distortion of Cr³⁺ (entering the Al³⁺ site in the host crystal) center in α-RbAl(SO₄)₂·12H₂O is induced mainly by the oxygen (or water) octahedron around the Cr³⁺ ion rather than the more distant neighbors.
The results of investigations related to physico-chemical properties, synthesis and structure of polyoxometalates and their lanthanide(III) complexes are briefly reviewed. Useful techniques for the verification of polyoxometalate compositions and the determination of components are compared. Complexation of metal ions, especially of lanthanide(III) ions, with polyoxometalates using absorption (in the UV-visible and the near IR region) and luminescence spectroscopy methods are presented. Absorption hypersensitive transitions of certain lanthanide(III) ions and laser-induced europium(III) ion luminescence spectroscopy are shown to be useful in complexation investigations. The significance of some polyoxometalate complexes as potential magnetic resonance imaging agents and in biological studies as antiviral agents are discussed.
Conducting reticulate doped polymeric films containing BEDT-TTF iodide crystalline network were annealed in order to transform the crystallites into crystal phases with metallic conductivity. Measured optical absorption spectra show that annealing shifts the absorption band to higher frequencies and increases the transparency of the films. This behavior corresponds to the transformation of the α-phase into the superconducting α_{t}-phase observed in (BEDT-TTF)_{2}I_{3} single crystals.
The present work is devoted to investigation of optical absorption in pure Ca_4GdO(BO_3)_3 single crystals in the spectral range 0.2-1.1 μm induced under influence of the gamma quanta irradiation with absorbed dose 2 × 10^3 Gy. The effect of heating in air on the absorption spectrum of irradiated sample is also studied.
Binding properties of ethylenediaminedi(o-hydroxyphenyl)acetic acid (EHPG) with lanthanide(III) ions were studied using spectroscopic methods. Luminescence intensity and lifetime of the Tb(III) ion were measured in a wide pH range in order to characterize the Ln-EHPG complexation. The calculated hydration number of the Tb-EHPG system proved the replacement of six water molecules by the EHPG ligand in the inner coordination sphere of Tb(III). Energy transfer from Tb(III) to Eu(III) in the Tb(III)-EHPG-Eu(III) system indicated an existence of only monomeric form of the Tb-EHPG complex. Analysis of the ^1H NMR and FTIR spectra of the EHPG ligand and its complexes with lanthanide(III) ions confirmed the hexadentate manner of EHPG complexation with the lanthanides. The system of Dy(III)-EHPG, showing a linear dependence of luminescence intensity (λ_{em}=578 nm) of Dy(III) on its concentration, in the range of 3.3×10-7 to 1×10-5 mol. l-1, can be applied for spectrofluorimetric determination of Dy(III).
The heteropolyanions of Preyssler anion [NaP_{5}W_{30}O_{110}]^{14-} and its europium-encrypted derivative [EuP_{5}W_{30}O_{110}]^{12-} were prepared and spectroscopically characterized. The compositions of these heteropolyanions were verified based on the results from elemental and thermogravimetric analysis and the data of spectrophotometric determination of tungsten contents. Absorption in the UV-vis and IR region and luminescence spectra, as well as results of the laser-induced europium ion luminescence spectroscopy, obtained for solid complexes and their solutions, were analysed. Both in solid and solution the europium-encrypted derivative has three water molecules of hydration.
The spectroscopic properties of trivalent dysprosium (Dy^{3+}) doped LiNbO_{3} crystals have been investigated at various temperatures. Absorption, emission, excitation and lifetime measurements have been performed and discussed in the framework of Judd-Ofelt approach. The stimulated emission cross sections of the strongest transitions of Dy ^{3+} ion have been estimated. A stimulated emission has been demonstrated in the near infrared.
Optical absorption, emission and luminescence kinetics of Nd^{3+} centres in the new borate crystal with Sr_{4}B_{14}O_{25}:Nd (Nd content 0.2 wt.%) composition are investigated and analysed. The oscillator strengths (P_{theor} and P_{exp}) for observed absorption transitions and phenomenological intensity parameters Ω_t (Ω_2=1.59×10^{-20} cm^{-1}, Ω_{4} = 2.06 × 10^{-20} cm^{-1}, and Ω_{6} = 2.28 × 10^{-20} cm^{-1} were calculated based on the standard Judd-Ofelt theory. Using Ω_t parameters the radiative transitions rates (W_{r}), branching ratios (β) and radiative lifetime (τ_{rad}) for Nd^{3+} centres in the Sr_{4}B_{14}O_{25}:Nd crystal were calculated and analysed. Measured lifetime (τ_{exp} = 105 and 93 μs at T = 10 and 300 K, respectively) is compared with this calculated (τ_{rad} = 331 μs) and quantum efficiency for Nd^{3+} centres from ^{4}F_{3/2} emitting level in the Sr_{4}B_{14}O_{25}:Nd crystal is estimated (η ≅ 30%). Incorporation peculiarities and local structure of Nd^{3+} luminescence centres in the Sr_{4}B_{14}O_{25} crystal and corresponding glass with 4SrO-7B_{2}O_{3} composition are discussed on the basis of referenced X-ray diffraction data and presented results.
The results of comparative studies of the effect of hydrogenation upon structural and optical properties of the commercial soda-lime silicate glasses doped either with monovalent silver or copper have been presented. The samples were characterised by means of the scanning and transmission electron microscopy and the UV-VIS-IR absorption spectroscopy. It has been shown that the annealing of suitably ion-exchanged specimens in gaseous hydrogen atmosphere could be considered as an effective procedure for obtaining composite materials of expected properties correlated with the induced changes of the morphology of both the glassy matrix and the dopant.
Calcium fluoride crystals doped with various concentrations of PbF_{2} have been grown using the Bridgman technique. The optical absorption spectra reveal the characteristic UV absorption bands of the Pb^{2+} ions. The distribution of the Pb^{2+}-ions along four crystals has been investigated using the optical absorption method. Taking into account the relationship between the optical absorption coefficient and the concentration of the impurities in the samples, the effective segregation coefficient of the Pb^{2+} ions has been calculated. Our study shows that the effective segregation coefficient of the Pb^{2+} ions in CaF_{2} host depends on the dopant concentration, and varies between 0.85 and 1.15, for 0.5 mol%PbF_{2} and 3 mol%PbF_{2}-doped CaF_{2}, respectively.
The changes of the optical absorption spectra of Cr,Mg:YAG epitaxial film caused by high-temperature redox treatment are investigated by means of in situ spectroscopy. The spectra were registered in the visible and near-IR spectral regions at temperatures up to 1100 K. The kinetics of optical absorption changing were obtained in the temperature range from 936 K to 1091 K and were described by mathematical model connecting the chromium recharging process with oxygen vacancies diffusion. The parameters of the model were determined from the approximations of the experimental kinetics.
Optical-temperature investigations of stationary and photo-induced absorption in undoped and Al (or Ga) doped Bi₁₂SiO₂₀ crystals are discussed. In the wave-number range 22000-4000 cm¯¹ under temperatures from 80 to 650 K, peculiarities of thermochromic effect have been revealed and temperature dependences of intensity of bands forming photo- and thermochromic effects have been found. A correlation between these dependences and spectra of thermostimulated current is explained.
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