Search results for "absorption spectroscopy"
showing 10 items of 828 documents
Luminescence and absorption spectroscopy of Sn-related impurity centers in silica
2006
We report an experimental study on the absorption and luminescence spectra of oxygen deficient point defects in Sn-doped silica. The absorption band at 4.9 eV (B2β band) and the two related photoluminescence bands at ∼4.2 eV (singlet-singlet emission, S1 → S0) and at ∼3.2 eV (triplet-singlet emission, T1 → S0), linked by a thermally activated T1 → S1 inter-system crossing process (ISC), are studied as a function of temperature from 300 to 20 K. This approach allows us to investigate the dynamics properties of the matrix in the surroundings of the point defects and the effects of local disorder on the two relaxation processes from S1: the radiative channel to S0 and the ISC process to T1. We…
Luminescence of fluorine doped silica glass
2003
Abstract The role of fluorine doping on silica properties was studied by luminescence methods. Non-doped samples of the same preparation technology possess an absorption band at 7.6 eV on the level of 2 cm−1. A trace of this band in the fluorine-doped sample is on the level of 0.1 cm−1. In both samples 7.6 eV photons as well as ionizing irradiation (X-ray, electron beam) excite photoluminescence of so-called oxygen deficient centers with a blue (2.7 eV) and a UV band (4.4 eV). The luminescence of the fluorine doped sample increases with dose many times from the initial low level for the same excitation. Also, thermally stimulated luminescence appears after irradiation. The energetic yield u…
Synthesis and properties of new phosphorus-functionalized bithiophene materials
2003
The synthesis and reactivity of the novel dithieno[3,2-b:2',3'-d]-phosphole system and its potential use in polymeric sensory materials was investigated. Due to the nucleophilic nature of the phosphorus atom, these materials were found to be easily tunable. Classical reactions at the phosphorus center were performed to modify the electronic structure of the system and the corresponding changes were detected by UV/Vis and fluorescence spectroscopy. Depending on the oxidation state of the central phosphorus atom or its substitution pattern, the dithieno[3,2-b:2',3'-d]-phospholes show varying wavelengths for absorption and emission allowing to distinguish between different compounds by means o…
Reddening map around ? Orionis
1990
uvbyβ photometry has been done for early-type stars in the surroundings of the shell star α Ori. The reddening maps show the presence of irregularly distributed absorbing material.
Post UV irradiation annealing of E’ centers in silica controlled by H2 diffusion
2004
Abstract We investigate the isothermal annealing of E′ centers generated by UV photons (266 nm) of a pulsed Nd:YAG laser in two natural silica types differing for their OH content. Electron spin resonance and absorption spectra recorded at room temperature at different delays from the laser exposure evidenced a partial reduction of E′ centers, more pronounced in the wet silica. These post irradiation kinetics complete within 10 5 s, regardless the silica type, and they are consistent with a diffusion limited reaction between the E′ centers and the molecular hydrogen H 2 . Analysis of our data is done by theoretical fits using the Waite's equation and compared with the H 2 diffusion paramete…
Quantum Chemical Simulations of Excited-State Absorption Spectra of Photosynthetic Bacterial Reaction Center and Antenna Complexes
2011
The semiempirical ZINDO/S CIS configuration interaction method has been used to study the ground- and excited-state absorption spectra of wild type and heterodimer M202HL reaction centers from purple bacterium Rhodobacter sphaeroides as well as of peripheral LH2 and LH3 light harvesting complexes from purple bacterium Rhodopseudomonas acidophila. The calculations well reproduce the experimentally observed excited-state absorption spectra between 1000 and 17,000 cm(-1), despite the necessarily limited number of chromophores and protein subunits involved in the calculations. The electron density analysis reveals that the charge transfer between adjacent chromophores dominates the excited-stat…
Complete hyperfine Paschen-Back regime at relatively small magnetic fields realized in potassium nano-cell
2015
A one-dimensional nano-metric-thin cell (NC) filled with potassium metal has been built and used to study optical atomic transitions in external magnetic fields. These studies benefit from the remarkable features of the NC allowing one to use $\lambda/2$- and $\lambda$-methods for effective investigations of individual transitions of the K D_1 line. The methods are based on strong narrowing of the absorption spectrum of the atomic column of thickness L equal to $\lambda/2$ and to $\lambda$(with $\lambda = 770\un{nm}$ being the resonant laser radiation wavelength). In particular, for a $\pi$-polarized radiation excitation the $\lambda$-method allows us to resolve eight atomic transitions (in…
Collapse and revival of a Dicke-type coherent narrowing in potassium vapor confined in a nanometric-thin cell
2015
A nanometer-thin-cell (in the direction of laser beam propagation) has been elaborated with the thickness of the atomic vapor column varying smoothly in the range of $L = \unit[50-1500]{nm}$. The cell allows one to study the behavior of the resonance absorption over the $D_1$ line of potassium atoms by varying the laser intensity and the cell thickness from $L = \lambda / 2$ to $L = 2 \lambda$ with the step $\lambda/2$ ($\lambda =\unit[770]{nm}$ is the resonant wavelength of the laser). It is shown that despite the huge Doppler broadening ($>\unit[0.9]{GHz}$ at the cell temperature $\unit[170]{^{\circ}C}$), at low laser intensities a narrowing of the resonance absorption spectrum is observe…
Synchrotron-based Fourier transform spectra of the ν23 and ν24 IR bands of hexamethylenetetramine C6N4H12
2015
Abstract Hexamethylenetetramine (HMT), C6N4H12 is a spherical top with nine IR-active modes. Because of its relevance for astrophysics, we recorded the absorption spectra in the full range of its fundamental bands. In total, we detected eight fundamental bands and recently published the rotational analysis of the four most intense bands ( ν 19 , ν 20 , ν 21 , ν 22 ) located in the 1000–1500 cm−1 range as a support for astronomical searches (Pirali et al., 2014). While the CH stretch modes are unresolved broad features, in this article we report the analysis of the two remaining fundamental bands exhibiting rotationally resolved structures: ν 23 –GS and ν 24 –GS located at about 820 cm−1 and…
A phase change in X Persei
1991
We present a series of optical spectroscopic and infrared photometric observations of the Be/X-ray binary system X Per made over the last four years. Over this period the Hα line profile changed from emission to absorption, accompanied by a decrease in the infrared flux by over a magnitude and a flattening of the infrared spectrum. Such behaviour is consistent with the loss of the circumstellar disc or shell of material around the Be star and the reversion to a normal O/B-type star.