UV absorption spectra of glycine crystals, i.e. triglycine sulphate, selenate, diglycine sulphate as well as their deuterated analogues in solid state and aqueous solutions are given. Results are compared with the electronic transition energies calculated by LCAO INDO method for glycine molecule and ion, assuming their crystal geometry.
The optical absorption spectra of lithium sodium potassium sulphate doped Ni^{2+} ions at 300 and 77 K was recorded. The observed bands are assigned as transitions from the ground state ^{3}A_{2g}(F) to various excited triplet and singlet states of the Ni^{2+} ion in octahedral symmetry. The splittings observed for the bands ^{3}T_{1g}(F) and ^{3}T_{2g}(F) at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The oscillator strengths of the transitions were computed from the area under the curves. From a detailed analysis of the bands of the spectrum, the crystal field parameters B, C, Dq and ξ are evaluated.
Luminescence and transient absorption of the oxygen-deficient CdWO_{4} crystal were studied. The electron transitions from the excited state of the luminescence center to some higher energy state are responsible for the transient absorption observed. The scheme of luminescence center levels is proposed from the obtained experimental results.
We compare theoretically predicted, by means of ab-initio calculations, dielectric tensor and related experimental values obtained from Mueller-ellipsometry measurements of an insulating monoclinic (optically biaxial) crystal of Cu(H₂O)₂(en)SO₄, en=C₂H₈N₂. We concentrate on the static limit, ω→ 0.
Noisy, non-resolved emission spectra of the (0,0) 391.4 nm N_{2}^{+} molecular band are employed for the rotational (and in some case vibrational) temperature evaluation in different sources in the range of 320-7900 K when the apparatus function of the recording system is unknown. The following sources are examined: an ovoid-shaped transferred arc at atmospheric pressure, a low-pressure transferred arc, a high-voltage high-pressure electric discharge, a low-pressure radio-frequency discharge, and an atmospheric pressure laminar plasma jet. The described method is based on a normalization of the experimental spectrum with respect to the (0,0) band-head amplitude followed by a point-to-point comparison of the real spectrum with respect to a computer simulated spectrum using the best-square fit criterion. This criterion is found as the good one: the relative error on temperature evaluation had the same order of magnitude as the noise-to-signal ratio, even if the last one was relatively high. It was also found that the rotational and vibrational temperatures in the radio-frequency discharge are very different, which indicates an out of thermodynamic equilibrium characteristic of such a discharge. The proposed method of temperature evaluation is shown as quite precise and simple to use for even the non-spectroscopists.
The luminescence and transient absorption of PbWO_{4} crystals were studied. The electron beam (10 ns, E≈270 keV) was used as excitation source. The kinetics of luminescence is complicated - the prompt rise of luminescence intensity is followed by a slow (τ_{r}≈100 ns) rise. The luminescence decay at 80 K is nearly exponential with τ_{d}≈4.0- 4.5 μs. The decay kinetics of transient absorption at 3.5 eV can be described roughly by two exponents with time constants τ_{1}≈100 ns and τ_{2}≈4.0 μs. A common process responsible for absorption relaxation and luminescence rise is suggested. The luminescence center excitation occurs during recombination process via Pb^{2+} excited state formation and subsequent energy transfer to WO_{4}^{2-} group.
First experimental investigations on absorption and photoluminescence of the novel Hg_{3}TeCl_{4} monocrystals grown by the Bridgman method are reported. A comparison of the measurement results with theoretical band structure calculations of the Hg_{3}TeCl_{4} crystal confirmed that Hg_{3}TeCl_{4} is a wide-band-gap photoconductor (E_{g}= 3.64 eV at 24 K) with the effective masses of charge carriers characteristic for semiconductors. Energetic position of the main photoluminescence peak and its temperature dependence indicates the presence of an additional energy level in the energy gap which takes part in the radiative recombination process and whose origin was discussed.
CuCl nanocrystals were elaborated in a NaCl ionic matrix by doping the latter with copper powder during growth. Optical absorption measurements revealed nanocrystals with a mean size of order 32 Å. This is consolidated by the Raman scattering measurements which showed nanodomains of similar size. X-ray diffraction measurements indicate a good crystallinity of the matrix and confirm the presence of CuCl nanocrystals within our samples. The annealing effect at 300˚C showed an increase in CuCl nanocrystal size with annealing time and demonstrated clearly the existence of a compound containing copper within our samples.
Solid solution crystals (Lu_{x}Gd_{1-x})_2SiO_5 single doped with Sm^{3+} and Dy^{3+} were grown by the Czochralski method. Segregation coefficients Lu/Gd, melting temperatures and structures of solid solution crystals were determined for 0.15 ≤ x ≤ 0.8. It was found that for x ≥ 0.17 the crystals belong to the monoclinic system within a space group C2/c and their melting temperature diminishes monotonously from 1990C to 1780C when x decreases from 0.8 to 0.15. Disparity of ionic radii of Lu^{3+} and Gd^{3+} induces structural disorder that brings about an inhomogeneous broadening of spectral lines in absorption and emission spectra of incorporated luminescent Sm^{3+} and Dy^{3+} ions. Optical properties of obtained crystals were determined based on results of measurement of absorption and emission spectra and luminescence decay curves. Spectroscopic investigation revealed that Sm^{3+} doped crystals show intense emission distributed in the visible-near infrared region with the most intense band centred at 605 nm and characterized by a branching ratio of 0.43. Emission spectrum of Dy^{3+} doped crystals is dominated by a band centred at 575 nm and characterized by a branching ratio of 0.58. It has been concluded that the systems under study are potential laser materials able to generate visible emission upon GaN/InGaN laser diode pumping.
The p-spectrum method is a time domain spectroscopy-based technique for reflection analysis of materials (including explosives) that takes into account only part of the reflected signal, which is next analyzed via the Fourier transform. The method is limited to the frequencies of about 1.8 THz due to the pulse properties of our time domain spectroscopy setup. In this paper we theoretically prove that application of a shorter pulse can increase this frequency range up to 2.2 THz, that enables analysis of penthrite and octogen, two important explosives.
This paper presents an optical system for transmission spectral measurements in the terahertz range. The source of radiation is a tunable solid-state laser, which generates a narrow-band nanosecond pulses in the range 0.67-2.68 THz and based on optical parametric oscillator phenomenon. The signal is detected with a fast and sensitive hot electron bolometer. Principle of generation and detection of pulses as well as methodology of measuring spectral characteristics are presented. We compared the results obtained with the free-space setup, which is based on the optical parametric oscillator and hot electron bolometer, with a purged time domain spectroscopy system in the range of 0.7-2.2 THz.
Based on a previously proposed two-dimensional model of a polyacene crystal, the contributions to the electro-absorption signal from different points of the exciton Brillouin zone are calculated. They are shown to differ substantially both in amplitude and in shape. This makes electro-absorption spectra very sensitive to vibronic coupling. On the one hand, the new factor is a potential complication in theoretical interpretations. On the other hand, it favours electro-absorption spectroscopy as a promising experimental tool to study vibronic effects.
The optical properties of Tl_4InGa_3S_8 layered single crystals have been studied by means of transmission and reflection measurements in the wavelength region between 400 and 1100 nm. The analysis of the room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 2.40 and 2.61 eV, respectively. Transmission measurements carried out in the temperature range of 10-300 K revealed the rate of change of the indirect band gap with temperature asγ=-6.0×10^{-4} eV/K. The absolute zero value of the band gap energy was obtained as E_{gi}(0)= 2.52 eV. The dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico single-effective-oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength, and zero-frequency refractive index were found to be 5.07 eV, 26.67 eV, 8.82×10^{13} m^{-2}, and 2.50, respectively.
The comprehensive analysis of transmission spectra for light propagated through ITO/ZnO/CdS multilayers to solar cell active layer of CdTe is performed. Optimal thickness of ZnO high resistive oxide supplying minimal optical losses in CdTe solar cell working range was determined. We get the maximal light transmission to active layer for ZnO film with thickness of 230 nm. The advantages of glass superstrate for multilayer structure with ZnO upper layer is discussed in comparison with the structure with ITO upper layer. Calculation of transmittance for textured surfaces of top face of solar element showed significant minimization of optical losses in the structure with ITO upper layer textured by inverted pyramids while for textured glass superstrate there is no ponderable profit as compared to multilayer structure with planar surface.
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.
Optical properties of TlGaS_{2x}Se_{2(1-x)} mixed crystals (0 ≤ x ≤1) have been studied using the transmission and reflection measurements in the wavelength range of 400-1100 nm. The optical indirect band gap energies were determined through the analysis of the absorption data. It was found that the energy band gaps increase with increase of sulfur atoms content in TlGaS_{2x}Se_{2(1-x)} mixed crystals. From the transmission measurements carried out in the temperature range of 10-300 K, the rates of change of the indirect band gaps with temperature were established for the different compositions of mixed crystals studied.
This paper presents detection, identification and quantification of gases using an infrared imaging Fourier-transform spectrometer. The company Telops has developed an imaging Fourier-transform spectrometer instrument, Hyper-Cam sensor, which is offered as short or long wave infrared sensor. The principle of operation of the spectrometer and the methodology for gases detection, identification and quantification has been shown in the paper, as well as theoretical evaluation of gases detection possibility. The variation of a signal reaching the imaging Fourier-transform spectrometer caused by the presence of a gas has been calculated and compared with the reference signal obtained without the presence of a gas in the imaging Fourier-transform spectrometer field of view. Some result of the detection of various types of gases has been also included in the paper.
VINΦ_{2}(TCNQ)_{2} is a salt with two different, non-parallel TCNQ stacks. The polarized reflectance spectra from single crystals in the IR region 660-5200 cm^{-1}, the powder absorption spectra 400-45000 cm^{-1} and FT-NIR Raman spectra of VINΦ_{2}(TCNQ)_{2} are measured at room temperature. Moreover, the temperature dependence of powder absorption spectra in the frequency range 400-7900 cm^{-1} are studied. The nature of electronic bands, the anisotropy of optical conductivity, the temperature dependence of some vibrational bands and the charge distribution on different TCNQ stacks are discussed.
The absorption spectrum of Bi_{12}SiO_{20}:Cu is measured in the spectral region 0.195-2.95 eV. The validity of the Urbach rule (2.08-2.95 eV) has been also verified. The photochromic effect of these samples in far IR region is investigated. The energy level diagram of Cu^{3+} cations in Bi-octahedrons is presented.
The present work is devoted to investigation of stability of stable color centers that are induced by gamma radiation in pure LiNbO_{3}, Cu-doped LiNbO_{3} and Ce-doped YAlO_{3} single crystals
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