Effect of Temperature on Luminescence of LiNbO3 Crystals Single-Doped with Sm3+, Tb3+, or Dy3+ Ions

Crystals of LiNbO3 single-doped with Sm3+, Tb3+, or Dy3+ and crystal of LiTaO3 single-doped with Tb3+ were grown by the Czochralski method. Luminescence spectra and decay curves for LiNbO3 samples containing Sm3+ or Dy3+ ions were recorded at different temperatures between 295 and 775 K, whereas those for samples containing Tb3+ ions were recorded at different temperatures between 10 and 300 K. Optical absorption spectra at different temperatures were recorded within the UV-blue region relevant to optical pumping of the samples. It was found that the effect of temperature on experimental luminescence lifetimes consists of the initial temperature-independent stage followed by a steep decrease with the onset at about 700, 600, and 150 K for Sm3+, Dy3+, and Tb3+ ions, respectively. Additionally, comparison of temperature impact on luminescence properties of LiNbO3:Tb3+ and LiTaO3:Tb3+ crystals has been adequately described. Experimental results were interpreted in terms of temperature-dependent charge transfer (CT) transitions within the modified Temperature—Dependent Charge Transfer phenomenological model (TDCT). Disparity of the onset temperatures and their sequence were explained based on the location of familiar zigzag curves connecting the ground state levels of rare earth ions with respect to the band-gap of the host. It was concluded also that LiNbO3:Sm3+ is suitable as an optical sensor within the 500–750 K temperature region whereas LiNbO3:Dy3+ offers the highest sensitivity at lower temperatures between 300 and 400 K.

Synthesis and Characterization of Catecholato Copper(II) Complexes with Sterically Hindered Neutral and Anionic N3 Type Ligands: Tris(3,5-diisopropyl-1-pyrazolyl)methane and Hydrotris(3,5-diisopropyl-1-pyrazolyl)borate

Three catecholato copper(II) complexes, [Cu(catCl4)(L1′)], [Cu(catBr4)(L1′)], and [Cu(catCl4)(L1H)], supported by sterically hindered neutral and anionic N3 type ligands: tris(3,5-diisopropyl-1-pyrazolyl)methane (referred to as L1′) and hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (referred to as L1−), are synthesized and characterized in detail. Their X-ray structures reveal that both [Cu(catCl4)(L1′)] and [Cu(catBr4)(L1′)] complexes have a five-coordinate square-pyramidal geometry and [Cu(catCl4)(L1H)] complex has a four-coordinate square-planar geometry. The L1H is unusual protonated ligand that controls its overall charge. For the three catecholato copper(II) complexes, the oxidation state of copper is divalent, and catechol exists in catecholate as two minus anion. This difference in coordination geometry affects their d-d and CT transitions energy and ESR parameters.

Synthesis, crystal structure and photoluminescence of [NHEt3][Re(I)(quinaldate)(CO)3Cl]

The salt [NHEt3][Re(I)(quinaldate)(CO)3Cl] was obtained by the reaction of Re(CO)5Cl with quinaldic acid and triethylamine in toluene. The crystal structure analysis of this salt revealed the presence of the complex anion [Re(quinaldate)(CO)3Cl]−, with the d6 Re(I) metal center in a pseudo-octahedral environment. The electronic spectra in absorption and emission exhibit bands which are attributed to quinaldate IL and CT transitions at comparable energies. The longest-wavelength emission originates from a Re(I) to quinaldate MLCT triplet, which can be quenched in solution by oxygen or triethylamine.

DFT STUDIES ON ELECTRONIC STRUCTURES AND THIRD-ORDER NONLINEAR OPTICAL PROPERTIES OF A SERIES OF Pt–Pt BOND-CONTAINING METAL COMPLEXES

In this paper, electronic structures and third-order nonlinear optical (NLO) properties of a series of Pt–Pt bond-containing metal complexes have been calculated by using the density functional theory (DFT) combining with the sum-over-states (SOS) method. In order to check the reliability of this method, the electron correlations and basis sets have been compared. Our calculated results show that introduction of electron donor, thiophene ring and lengthing of organic conjugated ligand can enhance third-order NLO responses. The electronic structure analysis shows that the [Pt–Pt(H2P(CH2)PH2)2] fragment displays strong electron-withdrawing character in these systems. Meanwhile, the third-order NLO response of Pt–Pt bond also has been estimated by using TDDFT–SOS method. An enhancement of third-order NLO response has been observed because of the introduction of the Pt–Pt bond. This is mainly due to the intense and low-lying metal-to-ligand charge transfer (MLCT) and intraligand (IL) CT transitions.

Photoswitching of Redox Potentials and Spectroscopic Properties in the UV/vis Region

The photoswitching of optical and electrochemical properties of di-donor, di-acceptor and donor-acceptor substituted photochromic tetrahydropyrene - [2,2]metacyclophanene and dihydropyrene - [2,2]metacyclophanediene systems has been studied theoretically. A switching of the halfwave oxidation and reduction potentials should be possible in the case of bis(pyridinium) and bis(hydroxyphenyl) substituted systems. Because of the relatively great perturbation of the planarity of the π-electron systems by large torsion of the substituents out of the π-electron structure of the photochromic system and the stair-like structure of the ring-opened isomer, relatively large excitation energies for CT transitions have been calculated with the AM1-CI procedure. The ring-closed structures should absorb in the visible spectral region, and the open-ring isomers should have a longest-wavelength absorption in the UV region.

Darstellung, Eigenschaften und elektronische Raman-Spektren von Di(bromo)phthalocyaninatometallaten(III) der Eisengruppe / Synthesis, Properties and Electronic Raman Spectra of Di(bromo)phthalocyaninatometalates(III) of the Iron Group Elements

Low spin di(bromo)phthalocyaninatometalates of tervalent iron, ruthenium and osmium ([MBr2Pc2-]-) are formed by the reaction of [FeBrPc2-] or H[MBr2Pc2-] (M = Ru, Os) with excess bromide in DMF or THF and isolated as (nBu4N)+ salts. The electronic spectra show the typical π- π*- transitions (B, Q, N region) of the Pc2- ligand together with a number of extra bands due to trip-multiplett and (Pc, Br → M)CT transitions. νs(MBr) is observed in the resonance Raman (RR) spectrum (RR enhanced for M = Fe, Ru) at 161 cm-1 (Fe), 183 cm-1 (Ru) and 192 cm-1 (Os), νas(MBr) at 251 cm-1 (Fe), 234 cm-1 (Ru) and 218 cm-1 (Os) in the FIR spectra. The RR spectra obtained by excitation at low absorbance between the B and Q region are dominated by the intraconfigurational " Γ7 →Γ 8" transition due to spin orbit splitting of the 2T2g ground state for Fe at 583 cm-1, Ru at 1026/1050 cm-1 and Os at 3131 cm-1 . In the MIR resp. NIR spectra vibronically induced transitions are observed for the Ru or Os complex.

Die Schwingungsfeinstruktur der elektronischen Absorptionsspektren von [OsO2(ox)2]2 -und [OsO2(mal)2]2-/ Vibrational Fine Structure on the Electronic Absorption Spectra of [OsO2(ox)2]2-and [OsO2(mal)2]2-

The complexes (TBA)2[OsO2(ox)2] and (TBA)2[OsO2(mal)2] have been prepared and characterized. The IR and Raman frequencies are assigned according to point group D2h. The electronic absorption spectra measured on thin films of the solid complex salts on silica discs at 10 K show well resolved vibrational fine structure. Two very weak bands (ε: 4-58) in the visible region are assigned to d-d transitions from the singlet ground state ag2 (dxy) to a triplet and singlet term of the equivalent π* orbitals b2g/b3g (dxz, dyz). The two more intense band systems (ε: 500-1500) in the UV region are attributed to CT transitions from b2u/b3u π orbitals of the oxo ligands to the lowest unoccupied orbitals b2g/b3g of the central ion. These electronic transitions couple with vs(Os = O) as indicated by the main progression of about 700 cm-1 . In comparison to the vibrational ground state this lowered frequency is caused by population of antibonding π levels. The loosening of the Os = O bonds in the excited state is demonstrated by high anharmonic constants (-2.5 to -10.5 cm-1) and the estimated bond lengthening of about 12 pm. Moreover the vibrational fine structure of the malonato complex shows many combination modes of vs(Os = O) with other symmetric fundamentals. Due to lower site symmetry in the solid state the CT transitions of the malonato compound are split into 2 components with a spacing of about 200 cm-1 .

Spectral behaviour and solvent effects of some aminoanthraquinone dyes

The electronic absorption spectrum of each of nineteen AAQ dyes has been studied in nine different organic solvents. The acid dissociation constants of dyes containing OH, COOH, or SO3H groups have also been determined experimentally. The spectra in ethanol display five bands in the uv region and one in the visible region (450–560 nm). This band is assigned to CT transitions of the type l–aπ which result from the interaction of the lone pair of the nitrogen atom with the phenyl ring of the carbonyl group. The CT nature of the band was supported theoretically and by the effect of solvent on band position.