Absorption Spectra Of Crystals Research Articles

Annealing and photobleaching effects on the absorption spectra of gamma-irradiated BaFI crystals

We have studied processes induced in gamma-irradiated BaFI crystals by illumination and thermal annealing and identified defect centers responsible for the observed absorption bands. We assign the 205-nm absorption band to α(F−) centers, the 230-nm band to α(I−) centers, the 270-nm band to Fi0 centers, the 370-nm band to Ii0 centers, the bands around 480 nm to F(F−) centers, and the 610-nm band to F(I−) centers. The proposed assignment accounts well for the radiation-induced processes identified in the crystals.

Electrolytic coloration and spectral properties of natural fluorite crystals containing oxygen impurities

Natural fluorite crystals containing oxygen impurities are colored electrolytically by using a pointed cathode and a flat anode at various temperatures and voltages. F and F 2 color centers are produced in colored fluorite crystals. O 2−–V a +, O 2−–V a + aggregate, Yb 2+, Ce 3+ and Sm 2+ absorption bands are observed in absorption spectra of uncolored fluorite crystals. O 2−–V a +, O 2−–V a + aggregate, Yb 2+, Ce 3+, Sm 2+, F, M (F 2) absorption bands and group of four absorption bands are observed simultaneously in absorption spectra of colored fluorite crystals. Current−time curve for electrolytic coloration of natural fluorite crystal and its relationship with electrolytic coloration process are given. Production and conversion of color centers are explained.

Effect of a magnetic field on radiation strengthening of LiF crystals

The variations in the yield stress and optical absorption spectra of LiF crystals subjected to simultaneous action of a weak magnetic field (B = 0.7 T) and X-ray radiation have been studied. At very low (up to 15 min) exposure doses, the weakening effect of the magnetic field has been observed. No noticeable change in the electronic spectra, in particular, in F-center generation, is caused by a magnetic field.

Influence of the substitution of the central Me atom in ammonium oxyfluorides on phase transitions: IR spectroscopy study

Comparative investigations of infrared absorption spectra of ion-molecular crystals of the ammonium-containing oxyfluorides (NH4)3WO3F3 and (NH4)3MoO3F3 have been performed. It has been found that the parameters of the vibrational spectra exhibit anomalies in the ranges of internal vibrations of the MeO3F3 octahedral groups and ammonium ions near the phase transition temperatures. A comparative analysis of the IR spectra allows us to affirm that the studied phase transition in (NH4)3WO3F3 is primarily associated with the ordering of octahedral groups, whereas in (NH4)3MoO3F3, it is mainly due to the ordering of ammonium groups and the distortion of ammonium ions by the crystal environment.

A new pseudo rubrene analogue with excellent film forming ability

A novel pseudo rubrene analogue, 6,11-di(thiophen-2-yl)-tetracene-5,12-dione (DTTDO) was synthesized, in which two thienyl groups and two carbonyl groups replacing four phenyl groups in the rubrene molecule were connected to the backbone of tetracene. This compound was characterized by single crystal X-ray structure analysis, thermogravimetric analysis, absorption spectra and electrochemical measurements. Unlike rubrene, DTTDO exhibited excellent film forming ability by normal vacuum deposition, indicating its promising applications in organic thin film transistors.

Electronic Spectra and Crystal Field Analysis of Energy Levels of Ho3+ in HoF63−

The electronic absorption spectra of single crystals of Cs(2)NaHoF(6) have been recorded in the spectral region between 4700 and 42000 cm(-1) at temperatures down to 10 K. The structure in the (5)I(8) → (5)I(J) (J = 7-4), (5)F(J) (J = 5-1), (5)S(2), (5)G(J) (J = 4-6), (3)K(J) (J = 7, 8) transitions has been analyzed and assigned. The emission spectra (5)S(2) → (5)I(J) (J = 6-8) and (5)G(4) → (5)I(J) (J = 5-7), (5)F(5) have also been recorded at 10 K for crystals of Cs(2)NaHoF(6) and partly also for samples of Cs(2)NaHoF(6):Yb(3+). The spectra comprise magnetic dipole zero phonon lines and electric dipole allowed one-phonon vibronic sidebands. From the detailed interpretation of the emission and absorption spectra, aided by a clear understanding of the vibrational behavior of the HoF(6)(3-) moiety and by magnetic dipole intensity calculations, a data set of 59 energy levels spanning 17 multiplet terms was derived. Crystal field calculations were then performed using a 4f(10) basis, as well as including the configuration interaction with a p-electron configuration. The latter calculation, which employed 14 parameters, gave better agreement with experiment and the mean deviation was 13.5 cm(-1). A comparison with the energy level fittings for Cs(2)NaHoCl(6) has been included. The crystal field parameters for the fluoro- and chloro-systems followed empirically predicted ratios.

Be-composition effect on structure, electronic and optical properties of BexZn1−xO alloys**Project supported by the National Natural Science Foundation of China (Grant Nos. 10974139 and 10964002), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050610010), the Science-Technology Foundation of Guizhou Province of China (Grant Nos. [2009]2066, [2009]06 and [2010]2146), the Project of Aiding Elites'

This paper carries out first principles calculation of the structure, electronic and optical properties of BexZn1−xO alloys based on the density-functional theory for the compositions x = 0.0, 0.25, 0.5, 0.75, 1.0. The lattice constants deviations of alloys obey Vegard's law well. The BexZn1−xO alloys have the direct band gap (Γ-Γ) character, and the bowing coefficients are less than the available theoretical values. Moreover, it investigates in detail the optical properties (dielectric functions, absorption spectrum and refractive index) of these ternary mixed crystals. The obtained results agree well with the available theoretical and experimental values.

Induction and inversion of chirality in poly-L -lysine and methyl orange complex

The mechanism of complexation of poly-L-lysine (PLL) with methyl orange (MO) and the appearance of induced circular dichroism (ICD) were investigated as a function of dye concentration and temperature and compared with that of the PLL-ethyl orange complex. The formation of stoichiometric complexes with uniform size and intensities of ICDs depended on the length of alkyl groups (methyl and ethyl) as determined from quartz crystal microbalance measurement, absorption spectra, and CD spectra data. Furthermore, at constant PLL concentration, a dependence of the inversion of the ICD on the MO concentration (CMO) was observed in the PLL-MO complexes, which to our knowledge has not been reported for a constant dye concentration system. The positive ICD in the PLL-MO complexes observed at CMO lower than 2.0 × 10−5 M showed reversible changes in response to heating and cooling, whereas the negative ICD in PLL-MO complexes observed at higher CMO inverted to positive ICD values in response to a decrease in temperature. These results demonstrate the alkyl group substituent in the dye, dye concentration, and temperature play important roles in the formation of PLL-azo dye complex and ICD appearance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Up-conversion emission in triply-doped Ho 3+/Yb 3+/Tm 3+ KGd(WO 4) 2 single crystals

Detailed spectroscopic studies of the triply doped KGd(WO 4) 2:Ho 3+/Yb 3+/Tm 3+ single crystals (which exhibit multicolor up-conversion fluorescence) are reported for the first time. The absorption spectra of crystals were measured at 10 and 300 K; the room temperature luminescence spectra were excited at 980 nm wavelength. The dependence of the intensity of luminescence on the excitation power for three different concentration of Ho 3+, Yb 3+ and Tm 3+ ions was investigated. Efficient green and red up-converted luminescence of Ho 3+ ions and weak blue up-conversion luminescence of Tm 3+ ions were observed in spectra. The red emission of Ho 3+ ions is more intensive than their green emission. Dependence of the up-conversion luminescence intensity on the excitation power and impurities concentration was also studied; the number of phonon needed for efficient up-conversion was determined for each case. All possible energy transfer processes between different pairs of the impurity ions' energy levels are also discussed.

Optical Energy Gap of Ti:Al2O3 Single Crystals

The optical absorption spectra of single crystals of titanium doped sapphire (Ti:A1203) with two different doping concentration (0.1% wt. and 0.25% wt.) have been recorded in the UV-visible spectroscopy at room temperature. It was observed that both crystals start to show strong absorptions around 325 run. From this spectrum attempt was made to estimate the values of energy gap and the type of transition occurs in Ti:A1203o From the analysis it show that the optical energy gap are 5.57 eV for 0.1% wt. Ti and 5.94 eV for 0.25 wt.% Ti and it a direct band gap transition.

Coupling of Frenkel excitons, charge transfer excitons and vibrations in linear absorption spectra of polyacene crystals

The linear absorption spectra of the crystals of anthracene, tetracene, and pentacene have been calculated in the case of coupling between Frenkel excitons (FEs), charge transfer excitons (CTEs) and intramolecular vibrations. The model and its parametrization for FEs and CTEs in the (a,b) plane of those crystals, first developed by Petelenz et al. have been used in the numerical simulations of the linear absorption. The calculated excitonic and vibronic spectra allow us to draw two main conclusions. First, CTEs and their vibronics will manifest themselves in the linear absorption of light polarized along the monoclinic axis only (i.e. for tetracene and pentacene along the crystallographic b-axis). Second, the vibronic coupling (FE-phonon and CTE-phonon) emphasizes and increases the number of the maxima due to CTEs manifested in the linear absorption.

Dynamics of the transformation of bistable centers and lattice in CdF2 crystals under femtosecond pulsed photoexcitation

The kinetics of photoinduced absorption spectra of CdF2 crystals with bistable indium and gallium centers under femtosecond pulsed excitation has been experimentally investigated. Based on the example of indium ions, it is shown that the transmission band in the absorption spectrum of deep centers is formed for 0.8–1 ps, which significantly exceeds the photon absorption time. This process is interpreted as a result of displacement of indium ion from the initial interstitial position to a site of neighboring unit cell; the displacement velocity is estimated to be 200–250 m/s, a value close to the thermal velocity of this ion at room temperature. The times characteristic of the formation of free polarons as a result of the displacement of neighboring lattice ions have been experimentally estimated for the first time at a level of 0.8–1.2 ps. The capture times of free polarons by trivalent gallium and indium ions are estimated (5 and 10 ps, respectively), as well as the corresponding cross sections (2 × 10−16 and 8 × 10−16 cm2).

Optical absorption spectra of tourmaline crystals from Altay, China

Tourmaline is an important functional and gem material. The current study examines pink, green, and brownish-green tourmalines from Altay deposit. Based on X-ray fluorescence (XRF) quantitative analyses and ultrariolet-visible-near-infrared (UV-VIS-NIR) spectral analyses in combination with annealing experiments, the color center of tourmaline is found to be related to the d-d transitions of ions or the d-d transitions of exchange coupled ions. Annealing treatment affects the color improvement of tourmaline crystals.

X-ray Crystallography of A Metalloprotein: A Reaction Intermediate of Heme Oxygenase

X-ray crystallographic analysis of a metalloprotein requires knowing the electronic state of the metal center, if one wants to elucidate the exact function and/or reaction mechanism. As an example, we show our recent structural analysis of the heme oxygenase reaction intermediate which is involved in the third step of the heme degradation reaction. The reaction intermediate was crystallized under anaerobic condition, and the obtained crystals were frozen into liquid nitrogen. The absorption spectra of the single crystal before and after X-ray irradiation were compared with that of the frozen solution in 100 K cold nitrogen stream. The determined structure offers the first solid evidence for the presence of a water cluster in the distal pocket of this catalytically critical intermediate. This structure combined with the QM/MM calculation supports our proposal that the biliverdin is produced via Fe-OOH verdoheme intermediate.

Aroylhydrazone derivative as fluorescent sensor for highly selective recognition of Zn2+ ions: syntheses, characterization, crystal structures and spectroscopic properties

A new Zn(2+) fluorescent chemosensor N'-(3,5-di-tert-butylsalicylidene)-2-hydroxybenzoylhydrazine (H(3)L(1)) and its complexes [Zn(HL(1))C(2)H(5)OH](∞) (1) and [Cu(HL(1))(H(2)O)]CH(3)OH (2) have been synthesized and characterized in terms of their crystal structures, absorption and emission spectra. H(3)L(1) displays high selectivity for Zn(2+) over Na(+), K(+), Mg(2+), Ca(2+) and other transition metal ions in Tris-HCl buffer solution (pH = 7.13, EtOH-H(2)O = 8 : 2 v/v). To obtain insight into the relation between the structure and selectivity, a similar ligand 3,5-di-tert-butylsalicylidene benzoylhydrazine (H(2)L(2)), which lacks the hydroxyl group substituent in salicyloyl hydrazide compared with H(3)L(1), and its complex [Zn(2)(HL(2))(2)(CH(3)COO)(2)(C(2)H(5)OH)] (3), [Co(L(2))(2)][Co(DMF)(4)(C(2)H(5)OH)(H(2)O)] (4), [Fe(HL(2))(2)]Cl·2CH(3)OH (5), have also been investigated as a reference. H(3)L(1) exhibits improved selectivity for Zn(2+) compared to H(2)L(2). The findings indicate that the hydroxyl group substituent exerts an effect on the spectroscopic properties, complex structures and selectivity of the fluorescent sensor.

Judd–Ofelt spectroscopic study of Mg/Er-codoped near-stoichiometric LiNbO3 crystals for integrated optics

Near-stoichiometric (NS) (Mg:)Er:LiNbO3 crystals were grown from melts containing 0.0/0.5, 0.5/0.5, and 1.0/0.5 mol%/mol% MgO/Er2O3. Crystal composition and optical properties studies show that the Li2O contents in these crystals increase all by ∼1 mol% relative to the congruent point. The 1.0 mol% MgO-doped NS crystal is just near optical damage threshold and withstands a 488 nm light intensity >0.74 MW/cm2 without optical damage. Unpolarized absorption spectra of these NS crystals were measured, and the Er3+ absorption cross-section spectra were determined. The Er3+ spectroscopic properties were studied by Judd–Ofelt theory. The results show that as the crystal composition approaches the stoichiometry, the Er3+ spectroscopic properties change definitely. The Er3+ ion in the NS crystal has smaller absorption cross section and hence weaker oscillator strength, lower emission rate, and longer radiative lifetime. Nevertheless, the radiative quantum efficiency is retained. In addition, the MgO codoping has less effect on the Er3+ spectroscopic properties.

Absorption and Circular Dichroism Spectra of La3Ga5SiO14 Crystals Doped with Pr3+, Ho3+, and Er3+ Ions

The absorption and circular dichroism (CD) spectra of La3Ga5SiO14 langasite crystals doped with Pr3+, Ho3+, and Er3+ ions have been studied in the wavelength range of 350–700 nm. The electronic transitions of these ions, which replace La3+ ions in the 3e position with the symmetry 2, are observed in the spectra. All transitions are active in both the absorption and CD spectra. The dipole strengths D om, rotational strengths R om, and anisotropy factors g have been calculated for well-resolved bands. Some features are noted for the spectra that were obtained, and their relationship with the structure disorder is considered

Spectroscopic and upconversion properties of erbium-doped potassium lithium tantalate niobate crystals under 800 nm femtosecond laser excitation

The single crystals of tungsten bronze-type potassium lithium tantalate niobate doped with three concentrations erbium with good quality are grown using top-seed solution growth method. The unpolarized ultraviolet-visible-near infrared optical absorption spectra of these single crystals are measured at room temperature. The green and red upconversion emission properties are analyzed with respect to steady-state spectra and decay behaviors under 800 nm femtosecond laser excitation. The spectroscopic properties of Er3+ ions are studied on the basis of the Judd–Ofelt theory. 12 Er3+ ions absorption bands are observed ranging from 350 to 1650 nm, the lower limit is also the ultraviolet absorption edge of these crystals. The fluorescence branching ratio and radiative lifetime are calculated to support the upconversion mechanism. The relationship of the Judd–Ofelt parameters Ω4<Ω6 of Er3+ in these crystals is different from the general trend Ω2>Ω4>Ω6. Experimental results indicate that upconversion emission is a two-photon process. It follows that the shortening of lifetime and the increasing of intensities of red emission are due to the increase in Er3+ ions cluster sites. Excited state absorption and energy transfer processes lead to the green emission while cross relaxation process produces the red emission.

Comparison of CW THz Wave Spectrometer with Laser Diode Excitation and Pulsed THz Wave Spectrometer with Cr:forsterite Sources Based on Difference Frequency Generation of Near-infrared Lasers in GaP

We constructed two types of terahertz (THz) spectrometers with automatic scanning control based on the difference frequency generation method by the excitation of the phonon-polariton mode in GaP. The pulsed THz wave spectroscopic systems were based on an optical parametric oscillator and Nd: YAG laser sources having a frequency resolution of 1.5 GHz, and on Cr:fosterite sources with a resolution of 20 GHz. Following these, we recently constructed a continuous wave (CW) THz wave spectroscopic system with laser diode excitation. One of the advantages of the CW THz wave spectrometer is its wide frequency tuning range with fine frequency resolution of < 8 MHz. In this study, we compare both types of spectrometers (pulsed versus CW) to show the characteristics of each system in terms of frequency resolution. The absorption spectra of a non-deformed white polyethylene crystal and ultra-high molecular weight polyethylene with/without deformation are measured by using the CW THz wave spectrometer and pulsed THz wave spectrometer. The effect of the high-resolution CW THz wave spectrometer is shown based on the THz spectroscopic results.

Control of absorption spectrum of a one-dimensional resonant photonic crystal

The crystal under consideration is a layered structure consisting of alternating layers of two materials, one of which is a resonantly absorbing gas. It is shown that the combination of the dispersion of an atomic gas with the dispersion of a photonic-bandgap structures allows one to efficiently control the transmission spectra of s- and p-polarized modes in these combined systems. It is found that the spectrum is highly sensitive to the position of the gas resonance frequency with respect to the bandgap edge and to a change in the gas pressure. The transmission, reflection, and absorption spectra of the resonant photonic crystal are studied at an angle of incidence equal to the Brewster angle of a seed photonic crystal. Possible applications of the found particular features of the dispersion of resonant photonic crystals are discussed.