An effective molecular orbital basis selection scheme to calculate resonant frequency-dependent polarizabilities and polarizability derivatives by time-dependent Hartee—Fock theory

A non-iterative method for calculating frequency-dependent polarizabilities is developed using time-dependent Hartrec—Fock theory. A simple procedure for selecting molecular orbitals and two-electron integrals in this method is proposed and shown to be effective in reducing computational effort.     

Analysis of propagation in a SELFOC fibre: The axial field component and the effect of multiple reflections

Based on the WKB solution of the wave equation, a discussion of the polarization rotation of Gaussian beams in focusing fibres is given. Near the focusing region the change of polarization has been found to be appreciable. The finite longitudinal size of fibres has been found to reduce the effective length of samples for wave focusing.     

Trapping parameters and kinetics in CaS: Ce,Cl luminophor

By means of thermally stimulated luminescence (TL) technique the trapping parameters and order of the kinetics in TL process in the CaS: Ce, Cl luminophor are investigated. In the temperature range 300–450 K, two glow-peaks are observed showing the presence of two group of traps in this luminophor whose trap-depths are 0.66 ± 0.16 eV and 1.13 ± 0.11 eV respectively as determined by three different methods. The order of the kinetics in TL processes in this luminophor comes out to be first order for the first group and second-order for the second group of traps.     

Photo- and electroluminescence of undoped and rare earth doped ZnO electroluminors

A series of undoped and rare earth (Dy, Yb, Nd, Pr, Gd, La, Sm and Er) doped ZnO electroluminors have been prepared and their photo-(PL) and electroluminescence (EL) spectra at different concertrations of rare earth ions have been investigated. PL and EL spectra of undoped electroluminors consist of three peaks. Due to the addition of the rare earth ions these peaks are shifted either to the longer or to the shorter wavelength side. The intensities are also either decreased or increased. Experimental results favour the donor—acceptor model for this system.     

A new method for the growth of Pb1−xSnxTe single crystals

Oriented bulk single crystals of lead-tin-telluride can be grown relatively easily on barium fluoride substrates by a vapor transport epitaxy technique. Both funnel shaped and cylindrical boules of varying Pb, Sn and Te compositions have been grown by this method. A growth rate of as much as 2g/day has been obtained. The crystals exhibit metallurgical and X-ray diffraction characteristics.     

Tight-binding calculations of surface states of Si(111)

Semi-empirical tight-binding calculations are reported for Si(111) surfaces. The calculations reproduce quantitatively the results obtained both experimentally and by more elaborate theoretical methods.     

Ferroelectric and paramagnetic properties of Li2Gd4 (MoO4)7 single crystals

Thermal behavior of such fundamental physical properties as polarization, pyroelectric current, dielectric constant and paramagnetic susceptibility are reported for dilithium heptamolybdotetragadolinate, Li₂Gd₄ (MoO₄)₇. The ferroelectric transition point has been determined by various methods and the results compared. The most reliable value of the Curie point has been obtained by the measurement of differential magnetic susceptibility as a function of temperature and is found to be 52±2°C. The room temperature values for the relative dielectric constant and paramagnetic susceptibility are 51.5 and 59.8 x 10^-6 cm³. g^-1, respectively. From the susceptibility measurements the values obtained for the Curie constant, C, and the paramagnetic Curie point, θp, are 1.79 x 10^-2 cm³ . g^-1 . deg and 247°K, respectively. It is believed that Li₂Gd₄ (MoO₄)₇ could be antiferromagnetic between 273 and 325°K.     

Singlet excited-state “energy hopping” in alkylbenzenes

The quenching of toluene fluorescence by cis-6-phenyl-2-hexene has been studied to determine the rate of singlet “energy hopping” in dilute solutions of alkylbenzenes. The singlet lifetime date have been analyzed by the Stern-Volmer method to give the quasi-isoenergetic rate, k_q, as 1.2 × 10¹⁰ M^?1?1. The result is consistent with an excimer formation dissociation mechanism for alkylaromatic singlet energy transfer in dilute solution.     

Charge transfer in keV proton collision with atomic oxygen: Differential and total cross sections

Classical Trajectory Monte Carlo method (CTMC) with the modal interaction potential [1] has been used to simulate the differential, total and partial capture cross sections in proton-oxygen atom collisions in the energy range of 0.5–200 keV. An interesting feature of the calculated differential cross sections (DCS) curve below the scattering angle 0.1^○ is the presence of oscillations showing asymmetry in angular positions. The oscillations in the partial cross sections are explained in terms of swapping effect. The DCS and total cross sections are found to be in good agreement with the experimental as well as other theoretical results.