Environmental broadening of the CTTS bands: the hexaammineruthenium(II) complex in aqueous solution

Cluster ab initio quantum chemistry approach is developed to simulate the charge-transfer-to-solvent (CTTS) absorption band and satellite ligand field bands of hexaammineruthenium(II) ion in aqueous solution. Several cluster models, including 16, 21, and 38 water molecules, are explored for this purpose. TDDFT method with long-range corrected BLYP (LC-BLYP) functional is used to obtain the vertical transition characteristics, and DFT B3LYP is used for calculation of the ground state geometry and vibrational frequencies of the solvated complex. A simple harmonic bath model is employed to estimate the absorption bandwidths and coherence decay times with the parameters taken from the quantum chemistry calculations. The present approach provides rather reasonable estimates for the CTTS band position and shape, also giving an additional insight for the mechanism of the CTTS band broadening.     

Aggregatively stable suspensions of micrometer powders of doped barium cerate for electrophoretic deposition of thin-film coatings of solid-oxide fuel cells

Potentialities of the method of electrophoretic deposition of thin-film coatings based on micrometer powders of multidoped barium cerate BaCe_0.8Sm_0.19Cu_0.01O_3–δ (BCSCuO) and BaCe_0.89Gd_0.1Cu_0.01O_3–δ (BCGCuO) were considered. Micrometer powders of BCSCuO and BCGCuO were produced by the methods of solid-phase and citrate-nitrate syntheses, respectively. The dispersity, fraction composition, and electrokinetic potential of nonaqueous suspensions of these powders and the electrokinetic parameters of the electrophoretic deposition process were examined. An ultrasonic treatment and ultracentrifugation produced aggregatively stable suspensions of BCGCuO and BCSCuO micrometer particles in a mixed (70/30 vol %) isopropanol–acetyl acetone medium. These suspensions are characterized by high positive values of the zeta potential (+24 and +28 mV, respectively). Thin film coatings of the electrolyte materials BCSCuO and BCGCuO, which are of interest for the technology of medium-temperature solid-oxide fuel cells, were produced by the electrophoretic deposition onto a dense model cathode.     

Simulation of structured 4T1→6A1 emission bands of Mn2+ impurity in Zn2SiO4: A first-principle methodology

A sequential, fully first-principle theoretical study of the Mn²⁺ green emission bands in the Zn₂SiO₄:Mn²⁺ phosphor is presented for the first time. A combined approach is developed based on the modern periodic density-functional theory and cluster ab initio wave-function-based electronic structure methods, the linear response theory for lattice phonons, and generating function formalism of vibronic spectra within the displaced multi-mode harmonic oscillator model. We obtain fairly good agreement between the calculated low- and high-temperature emission band positions, widths, zero-phonon lines and phonon wings and the available experimental emission studies, with special emphasis on Mn²⁺ distribution over two non-equivalent Zn²⁺ sites in the Zn₂SiO₄ material. An interpretation for vibronic structure observed in the low-temperature emission spectrum of this phosphor is suggested based on the present first-principle study.     

Ab initio study of phosphorescent emitters based on rare-earth complexes with organic ligands for organic electroluminescent devices

An ab initio approach is developed for calculation of low-lying excited states in Ln(3+) complexes with organic ligands. The energies of the ground and excited states are calculated using the XMCQDPT2/CASSCF approximation; the 4f electrons of the Ln(3+) ion are included in the core, and the effects of the core electrons are described by scalar quasirelativistic 4f-in-core pseudopotentials. The geometries of the complexes in the ground and triplet excited states are fully optimized at the CASSCF level, and the resulting excited states have been found to be localized on one of the ligands. The efficiency of ligand-to-lanthanide energy transfer is assessed based on the relative energies of the triplet excited states localized on the organic ligands with respect to the receiving and emitting levels of the Ln(3+) ion. It is shown that ligand relaxation in the excited state should be properly taken into account in order to adequately describe energy transfer in the complexes. It is demonstrated that the efficiency of antenna ligands for lanthanide complexes used as phosphorescent emitters in organic light-emitting devices can be reasonably predicted using the procedure suggested in this work. Hence, the best antenna ligands can be selected in silico based on theoretical calculations of ligand-localized excited energy levels.     

Theoretical investigations on the high light yield of the LuI3:Ce scintillator

The extremely high scintillation efficiency of lutetium iodide doped by cerium is explained as a result of at least three factors controlling the energy transfer from the host matrix to activator. We propose and theoretically validate the possibility of a new channel of energy transfer to excitons and directly to cerium, namely the Auger process when Lu 4f hole relaxes to the valence band hole with simultaneous creation of additional exciton or excitation of cerium. This process should be efficient in LuI₃, and inefficient in LuCl₃. To justify this channel, we perform calculations of density of states using a periodic plane-wave density functional approach. The second factor is the increase of the efficiency of valence hole capture by cerium in the row LuCl₃-LuBr₃-LuI₃. The third one is the increase of the efficiency of energy transfer from self-trapped excitons to cerium ions in the same row. The latter two factors are verified by cluster ab initio calculations. We estimate either the relaxation of these excitations and barriers for the diffusion of self-trapped holes (STH) and self-trapped exciton (STE). The performed estimations theoretically justify the high LuI₃:Ce³⁺ scintillator yield.     

Microwave heating of electrons of a dense plasma column at frequencies higher than electron cyclotron frequency

In the overdense collisionless plasma column inserted through the narrow sides of a rectangular waveguide, the excited electron cyclotron harmonic waves (CHWs) are studied by means of two movable probes and a phase interferometer in the range of parameters of 2 >ω/ω _ce >1; 0·5 < (ω _pe /ω)² < 15. Two kinds of CH waves have been found in the dipole mode:

1. Stable backward CH waves with the phase velocity in the direction from the axis to the periphery.
2. Unstable backward CH waves with the phase velocity in the opposite direction.

From the correlation measurements and amplitude distribution of the CH waves at the applied frequency and its second harmonic frequency it has been found that in the range of 2 >ω/ω _ce > >1·5 efficient nonlinear resonant interaction of CH waves takes place. The position of the loci of resonant interaction inside the plasma column has been found both experimentally and by a simple new graphical procedure for the resonant conditions of the formω ₂=2ω ₁; k₂=2¦k₁¦. In absence of this condition, no effective generation of the second harmonic frequency has been found. The resonant interaction of CHWs atω/ω _ce =1·85 is the cause of self-trapping of CH waves between the zones of resonant interaction in radial direction and of the anomalous heating rate of electrons.     

The Shift of the Peak of a Localized Plasmon Resonance in Granulated Gold Films on the Surface of a-C:H

Optics and Spectroscopy - Spectra of optical density of granulated 2-nm-thick gold films deposited on the surface of thin films of amorphous hydrogenated carbon (a-C:H) on quartz substrates are...     

Simulating the structureless emission bands of Mn2+ ions in ZnCO3 and CaCO3 matrices by means of quantum chemistry

Results from theoretical studies on the structureless luminescence spectra of Mn²⁺ impurity ions in matrices of calcite (CaCO₃) and smithsonite (ZnCO₃) are reported. The positions of the maxima and the width of the ⁴ T ₁(⁴ G) → ⁶ A ₁(⁶ S) emission bands of the indicated luminophors are calculated using a combined approach based on the periodic and cluster methods of quantum chemistry, and on well-known models of the vibrational broadening of electronic transition bands of impurity centers in crystals. The calculated parameters of the spectral bands are compared with the known experimental data and discussed in terms of the structural features of the investigated matrices and the contribution from lattice vibrations in the mechanism of broadening.