Electronic and Resonance Raman Spectra of a Multibridged Iron Porphyrin

Abstract

Reported are the electronic and resonance Raman (rR) spectra of a multibridged iron porphyrin derived from meso-tetra(4-pyridil)porphynate iron(II) by complexing the pyridine residues with [Ru^II(edta)]^2- ions. The polymetallated system exhibits the characteristic Soret band at 428 nm (log ε = 5.2) and a shoulder around 465 nm (4.6). The rR enhancement of the porphyrin vibrational modes is similar to those previously reported for typical porphyrins; however, an additional feature appears around 465 nm, associated with the selective enhancement of some pyridine vibrational modes. Based on the rR excitation profiles the absorption band at 465 nm was assigned to a Ru^II-to-pyridine dπ→Pπ? charge-transfer transition.     

Optical and Conductivity Studies of Cr3+ Doped Polyvinyl Pyrrolidone Polymer Electrolytes

Abstract

Polymer electrolyte films of polyvinyl pyrrolidone (PVP) embedded with various concentrations of Cr³⁺ ions were prepared by a solution casting technique. The complexation between the Cr³⁺ ions and the polymer was confirmed by Fourier transform infrared (FTIR) spectroscopy and UV–vis spectroscopy. The electrical conductivity of the films was measured using an impedence analyzer in the frequency range of 42?Hz to 5?MHz at ambient temperature. It was observed that the conductivity increased with the increase in the Cr³⁺ ion concentration. UV–visible absorption spectra in the wavelength range of 200–800?nm were used to determine the direct and indirect optical energy band gaps and optical absorption edge. Both of the optical band gaps decreased with the increase in Cr³⁺ ion concentration. FTIR studies on pure and Cr³⁺ doped PVP polymer films revealed the vibrational changes that occurred due to the effect of the dopant Cr³⁺ ions in the polymer. Our results suggested that Cr³⁺, as a dopant, is a good choice to improve the electrical properties of PVP polymer electrolytes.     

Sonochemiluminescence in an aqueous solution of Ru(bpy)3Cl2

The sonochemiluminescence spectra of electron-excited ions ^*[Ru(bpy)₃]²⁺ was registered for the first time during sonolysis of argon saturated aqueous solutions of Ru(bpy)₃Cl₂ with low concentration. At single-bubble sonolysis, the luminescence band of ruthenium is recorded at a concentration of Ru(bpy)₃Cl₂ from 10⁻⁶ M, and at multibubble from 10⁻⁵ M. Possible mechanisms for the appearance of the band of a tris-bipyridyl ruthenium(II) complex on the background of an structureless continuum of water in the spectra of sonoluminescence are analyzed. Based on the results of the comparison of the sonoluminescence spectra of Ru(bpy)₃Cl₂ aqueous solutions with the sonoluminescence spectra of aqueous solutions of rhodamine B (which has a high quantum yield of photoluminescence) it was established that a possible mechanism of sonophotoluminescence does not play a decisive role in ruthenium sonoluminescence. The effect of radical acceptors (O₂, C₂H₅OH, Cd²⁺, I⁻) on ruthenium sonoluminescence is analyzed. The most significant mechanism for the formation of electron-excited ions ^*[Ru(bpy)₃]²⁺ during sonolysis is the sonochemiluminescence in oxidation-reduction reactions involving [Ru(bpy)₃]²⁺ ions and radical products of sonolysis of water (OH, H, e⁻_aq) in the solution volume.     

57Fe Mössbauer spectroscopy on the cyclic spin-cluster Fe6(tea)6(CH3OH)6

We present ⁵⁷Fe Mössbauer spectroscopy experiments on the cyclic spin-cluster Fe₆(tea)₆(CH₃OH)₆ (tea = triethanolaminato(-3)). In former studies, the spin cluster has been treated as a homogenous, quasi-one-dimensional spin S=5/2 Heisenberg antiferromagnet. Our experiments reveal spectra, which consists of two different quadrupolar doublets. In consequence, there are two different Fe sites among the hexanuclear iron spin-cluster.     

VUV-UV excited luminescent properties of LnCa4O(BO3)3:RE (Ln=Y, La, Gd; Re=Eu, Tb, Dy, Ce)

Calcium lanthanide oxyborate doped with rare-earth ions LnCa₄O(BO₃)₃:RE³⁺ (LnCOB:RE, Ln=Y, La, Gd, RE=Eu, Tb, Dy, Ce) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos’ and Jφrgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. Jφrgensen, Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band E_ct were calculated and compared with their excitation spectra.Eu³⁺ and Tb³⁺ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce³⁺ ions do not show efficient luminescence and quench the luminescence of Tb³⁺ ions when Tb³⁺ and Ce³⁺ ions are co-doped into LnCOB. GdCOB doped with Dy³⁺ shows yellowish white light under irradiation of 254 nm light for the reason that Gd³⁺ ions transfer the energy from itself to Dy³⁺. Because of the existence of Gd³⁺, the samples of GdCOB:RE³⁺ show higher excitation efficiency than LaCOB:RE³⁺ and YCOB:RE³⁺, around 188 nm, which indicates that the Gd³⁺ ions have an effect on the host absorption and can transfer the excitation energy to the luminescent center such as Tb³⁺, Dy³⁺ and Eu³⁺.     

团簇六边形斑图等离子体参数的光谱测量

在氩气和空气混合气体介质阻挡放电中,首次发现了团簇六边形斑图。运用发射光谱法,研究了此斑图中单个团簇的三种等离子体参数：分子振动温度、分子转动温度以及电子的平均能量随空气含量的变化。实验通过测量氮分子光谱并采用氮分子第二正带系(C3Π_u→B 3Π_g)计算了振动温度;同时采集氮分子离子(N+₂)的第一负带系(B 2Σ+_u→X 2Σ+_g)计算转动温度。利用氮分子离子391.4 nm和激发态的氮分子337.1 nm两条发射谱线的相对强度之比,作为研究电子平均能量的变化的依据。结果显示,当混合气体中空气含量从16%逐渐增大到24%时,三种等离子体参数均逐渐增大。     

Luminescence quenching of [Ru(bpy)3] by ruthenium(II) tetraphosphite complexes with different phosphite ligands

The luminescence quenching of excited Tris(2,2-bipyridine)ruthenium(II) ions by trans-[RuCl₂{P(OR)₃}₄] complexes with different alkyl chain ligands (R=C₂H₅, C₂H₅Cl, ⁿC₄H₉, ⁱC₃H₇ o-tolyl and ^tC₄H₉) was investigated. None of the acceptor Ru(II) phosphite complexes were luminescent, and the rate constants of the bimolecular system were determined within the range of 1.15 and 0.28×10⁸ M⁻¹ s⁻¹ for R=C₂H₅ and ^tC₄H₉, respectively. The results indicate a direct effect of the alkyl chains in the rate constants, showing a decrease of k_q as a function of increased of the alkyl chains (R) in the ruthenium(II) tetraphosphite complexes. The greater the R group content in the phosphite ligand, the more difficult the electron transfer is.     

Enhance luminescence by introducing alkali metal ions (R+ = Li+, Na+ and K+) in SrAl2O4:Eu3+ phosphor by solid-state reaction method

In the present article, the role of charge compensator ions (R⁺?=?Li⁺, Na⁺ and K⁺) in europium-doped strontium aluminate (SrAl₂O₄:Eu³⁺) phosphors was synthesized by the high-temperature, solid-state reaction method. The crystal structures of sintered phosphors were in a monoclinic phase with space group P2₁. The trap parameters which are mainly activation energy (E), frequency factor (s) and order of the kinetics (b) were evaluated by using the peak shape method. The calculated trap depths are in the range from 0.76 to 0.84?eV. Photoluminescence measurements showed that the phosphor exhibited emission peak with good intensity at 595?nm, corresponding to ⁵D₀–⁷F₁ (514?nm) orange emission and weak ⁵D₀–⁷F₂ (614?nm) red emission. The excitation spectra monitored at 595?nm show a broad band from 220 to 320?nm ascribed to O–Eu charge-transfer state transition and the other peaks in the range of 350–500?nm originated from f–f transitions of Eu³⁺ ions. The strongest band at 394?nm can be assigned to ⁷F₀–⁵L₆ transition of Eu³⁺ ions due to the typical f–f transitions within Eu³⁺ of 4f⁶ configuration. The latter lies in near ultraviolet (350–500?nm) emission of UV LED. CIE color chromaticity diagram and thermoluminescence spectra confirm that the synthesized phosphors would emit an orange-red color. Incorporating R⁺?=?Li⁺, Na⁺ and K⁺ as the compensator charge, the emission intensity of SrAl₂O₄:Eu³⁺ phosphor can be obviously enhanced and the emission intensity of SrAl₂O₄:Eu³⁺ doping Li⁺ is higher than that of Na⁺ or K⁺ ions.     

Investigation of gain characteristics in mixed crystals LiMeF4 (Me = Y,Lu, Yb) doped by Ce3+ ions

Differential gain spectra in the range 295–335 nm were measured in crystals of scheelite structure LiY_{1 ? x} Lu _x F₄ (x = 0–1), doped by Ce³⁺ ions. It is shown that variation of Lu³⁺ and Y³⁺ ions relative content in LiY_{1 ? x} Lu _x F₄ crystals allows to manipulate the spectral width of the amplification band. Cross-sections of excited-state absorption at the wavelengths of Ce³⁺ luminescence, probability ratios of formation and thermal destruction of color centers depending on the Y³⁺ ions content in LiY_{1 ? x} Lu _x F₄ crystals were estimated. Even better gain characteristics have been demonstrated by LiLuF₄:Ce³⁺, doped by Yb³⁺ ions. The highest optical gain coefficient with a wide amplification band among studied samples was observed in LiLuF₄:Ce³⁺ crystal, codoped by Yb³⁺ ions.     

Infrared Spectra of Morfolonium (mpH)2Mo2Cl6(H20)2(I),(mpH)2Mo2ClxBr6-x(H2O)2(II)/ (mpH)2Mo2Br6(H2O)2(III) and the Pyridinium (PyH)2Mo2I6(H2O)2(IV)Hexahalo-di(aquo): dimolybdate(II) Complexes,Containing Quadruple Metal-Metal Bounds

Abstract

The electronic (800–400 nm), infrared (4000–200,400–20 cm^?1), ordinary Raman (400–200 cm^?1) spectra of morpholinium and the pyridium hexahalo-di(aquo) dimolybdate(II) complexes, containing quadruple metal-metal bonds were investigated. The electronic spectra of the solid compounds at various temperatures (25,100 and 300K) demonstrate intense and structured bands in the visible region (510–582 nm) attributed to the expected δ→δ? transitions.

From the infrared and Raman spectra, the skeletal stretching modes in these complexes have been localized, and the charectenstic bands of these ions were observed in the expected regions.

Finally, the ionic interections were relatively weak, but the existance of phenomena was perceptible and the result was obtained in agreement with X-ray data.     

Vibrational Analysis of the A3Π0−X1Σ+ and B3Π1−X1Σ+ Subsystems of the GaBr Molecule

Abstract

The emission band spectrum of gallium monobromide has been excited in a dc hollow cathode discharge. bands of the ³Π_0,1?X¹Σ⁺ system, lying in the range from 340 to 370 nm have been recorded at high resolution and measured. The previous vibrational analysis has been revised and corrected. New vibrational assignment has been proposed and improved vibrational constants of the upper and lower electronic states have been determined.     

Violet-blue-shift of emission and enhanced luminescent properties of Ca3(PO4)2:Ce3+ phosphor induced by substitution of Gd3+ ions

Ca₃(PO₄)₂:1mol%Ce³⁺/xGd³⁺ (where x = 0.5, 1.0, 3.0 and 5.0 mol%) phosphors were synthesized by the conventional combustion synthesis method. The X-ray diffraction patterns showed their rhombohedral structure with space group of R3c. The optical properties including reflectance, excitation and emission were investigated. The band gaps of the phosphors were calculated from diffuse reflectance spectra data using the Kubelka–Munk function. The photoluminescence (PL) excitation spectra exhibited the broadband 4f–5d transition of Ce³⁺ ions centered at ~265 nm. The PL emission properties of the Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphors were studied as a function of the Gd³⁺ ion concentration. The Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor had a wide emission band ranging from 320 to 400 nm, and peaking at 365 nm. This emission is ascribed to the transition from the higher 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. The 365 nm peak shifted to longer wavelengths with increasing concentration of the Gd³⁺ ion. The CIE chromaticity diagram of Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor showed tunable emission colour from violet to violet-blue, suggesting that this phosphor can act as a source of violet-blue colour for application in information displays, phototherapy and photoluminescent liquid crystal displays.     

Infrared and visible spectroscopic studies of the ytterbium doped borate Li6Y(BO3)3

The spectroscopic study of trivalent ytterbium doped Li₆Y(BO₃)₃ is conducted in the UV-visible and infrared range. An excitation in the charge transfer band of ytterbium has been selected in order to reduce the reabsorption effect on the IR emission intensity. The maximum of the emission is located at 972 nm for an excitation at 230 nm. The energy level assignment has been successfully conducted using vibrational spectroscopy to distinguish the pure electronic transitions from the phonon-assisted ones. The splitting of the ²F_5/2 and ²F_7/2 components is equal to 523 cm⁻¹ and 676 cm⁻¹, respectively. The decay time dependence as a function of the concentration is also reported. The calculated value τ_rad is about (1.03 ± 0.01) ms for the 1% doped material. For the highest concentration, an IR excitation gives rise to the observation of a blue-green luminescence caused by two mechanisms: an erbium emission at 550 nm after upconversion and a cooperative luminescence of ytterbium ions.     

A Vibrational Spectroscopic Study of the So-Called Healing Mineral Papagoite CaCuAlSi2O6(OH)3

ABSTRACT

Papagoite is a silicate mineral named after an American Indian tribe and was used as a healing mineral. Papagoite CaCuAlSi₂O₆(OH)₃ is a hydroxy mixed anion compound with both silicate and hydroxyl anions in the formula. The structural characterization of the mineral papagoite remains incomplete. Papagoite is a four-membered ring silicate with Cu²⁺ in square planar coordination.

The intense sharp Raman band at 1053 cm^?1 is assigned to the ν₁ (A _1g) symmetric stretching vibration of the SiO₄ units. The splitting of the ν₃ vibrational mode offers support to the concept that the SiO₄ tetrahedron in papagoite is strongly distorted. A very intense Raman band observed at 630 cm^?1 with a shoulder at 644 cm^?1 is assigned to the ν₄ vibrational modes.

Intense Raman bands at 419 and 460 cm^?1 are attributed to the ν₂ bending modes.

Intense Raman bands at 3545 and 3573 cm^?1 are assigned to the stretching vibrations of the OH units. Low-intensity Raman bands at 3368 and 3453 cm^?1 are assigned to water stretching modes. It is suggested that the formula of papagoite is more likely to be CaCuAlSi₂O₆(OH)₃ · xH₂O. Hence, vibrational spectroscopy has been used to characterize the molecular structure of papagoite.     

Optical properties of 3d-ions doped RbCdF3. Radiation effects

Abstract

The optical properties of RbCdF₃ crystals doped with Cr³⁺, Mn²⁺ and Ni²⁺ have been studied. Absorption and photoluminescence spectra correspond to these ions in an octahedral environment. The lifetimes of the emitting levels have been measured at different temperatures. Single exponential decays are obtained for Mn²⁺ and Ni²⁺ while a non-exponential decay is found in the case of Cr³⁺. Radiation effects have also been studied. A new absorption band is produced in the 305 nm region by RT X-irradiation. Exciting with light in this band the 3d-ions emissions are observed.     

Electronic and vibrational spectra of MnO2−4 in KBr crystals

Two new features have been observed in the electronic spectrum of KBr crystals doped heavily with MnO^2?₄ ions. The band at 870 nm is assigned to the crystal field transition e → t₂. The band at 600 nm shows a series of vibrational sub-bands at an interval of 740cm^?1 and is ascribed to the coupling between electronic transition and totally symmetric mode of the ion.A line at 830cm^?1, ascribed to totally symmetric mode v₁(A₁), has been observed for the first time in the Raman spectrum. I.R. spectrum of KBr: MnO^2?₄ shows four lines—one due to MnO^2?₄ in Td symmetry and the other three to the split components of v₃(T₂) for MnO^2?₄ in Cs symmetry. I.R. spectrum of KBr: MnO^2?₄: Ca²⁺ shows another s of four lines—one due to MnO^2?₄ in Td symmetry and the other three to the v₃(T₂) mode of the ion in C_2v symmetry. The v₁(A₁) line could not be observed in the i.r. spectra.     

Vibrational spectroscopic characterization of the magnesium borate-phosphate mineral lüneburgite

ABSTRACT

Lüneburgite, a rare magnesium borate-phosphate mineral from Mejillones, Chile, has been characterized using Raman and mid-infrared spectroscopy methods. Boron tetrahedra are characterized by sharp Raman band at 877?cm^?1, attributed to the ν₁[BO₄]^5? symmetric stretching mode. The phosphate anion is associated with a distinct band at 1032?cm^?1, attributed to the ν₃[PO₄]^3? antisymmetric stretching mode. The most intensive Raman band at 734?cm^?1 is ascribed to stretching vibrations of bridging oxygen atoms in boron–oxygen–phosphor bridges. Bonds associated with water bending mode and stretching vibration are observed at 1661?cm^?1 (infrared) and in the 3000–3500?cm^?1 region (Raman and infrared spectrum).     

Vibronic coupling and excited‐state reaction dynamics of pyrazine in 1 1B2u (1ππ*) state by resonance Raman spectroscopy and CASSCF calculation

The photophysics and photochemistry of pyrazine (C₄H₄N₂, D_2h) after excitation to the S₂ (1 ¹B_2u, ¹ππ*) electronic state were studied by using the resonance Raman spectroscopy and complete active space self‐consistent field method calculations. The B‐band resonance Raman spectra in cyclohexane solvent were obtained at 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of pyrazine in the S₂ (1 ¹B_2u, ¹ππ*) state. Three electronic states 1 ¹B_3u, 1 ¹B_1g, and 1 ¹B_2g were found to couple with the S₂ (1 ¹B_2u, ¹ππ*) state. Two conical intersection (CI) points CI[S₂(B_2u)/S₁(B_3u)] and CI[S₁/S₀] and one transition state of the isomerization between pyrazine and pyrimidine were predicted to play important roles in the photochemistry of pyrazine. On the basis of the calculations, the mechanism of the photoisomerization reaction between pyrazine and pyrimidine has been proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

V centers in single crystal Al2O3

From optical and thermal bleaching experiments it is concluded that the 400 nm absorption band which appears in Al₂O₃ after γ-irradiation is a composite V band. One of its components is attributed to the V^-_OH center which also is responsible for a localized vibrational band at 3316 cm^-11 analogous to the one observed for the V_OH center in MgO. The irradiation also results in electron trapping at Cr³⁺ impurity ions to produce a band at 227 nm. Annealing at 170°C destroys the V^-_OH center by releasing holes which convert the Cr²⁺ to Cr³⁺ with an attendant thermoluminescence.     

Spectroscopy and Kinetics of HgBr (B-X) Formation Due to Collisions of Helium Ions with Methyl Mercury Bromide Molecules

Abstract

Emission resulting from collisions of 100–1000 eV He· and He₂· ions with CH₃HgBr molecules has been characterized in the 244–580 nm region. Emission bands due to HgBr (B-X), CH(A-X), and CH(B-X) transitions were observed besides atomic mercury lines. Emission cross-sections as a function of energy of helium ions for the strongest band of HgBr radical at 502 nm corresponding to the transition (v' = 0 ? v′ = 22) were determined.