David J. Simkin
McGill University
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Featured researches published by David J. Simkin.
Journal of Chemical Physics | 1971
J. P. Larkindale; David J. Simkin
The magnetic circular dichroism (MCD) of six polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, 1,2‐benzanthracene, picene, and 1,2–3, 4‐dibenzanthracene) has been measured in the α (1Lb) absorption region. A band in the MCD spectrum of anthracene which does not correspond to any reported absorption band has been assigned to the hitherto unobserved α band. The sign and magnitude of the MCDs observed are in good agreement with those calculated using CNDO wave‐functions.
Journal of Luminescence | 1986
Pierre Menassa; David J. Simkin; Peter Taylor
Abstract The decay times and excitation spectra for the two characteristic luminescence bands of Mn 2+ are reported, and analysed. The analysis of the decay times indicates that the high energy emission band arises mainly from Mn 2+ centers in the Si-rich phase, while the low energy emission is principally due to Mn 2+ in the B-rich phase. An analysis of the excitation spectra results in the determination of crystal field parameters for each of the two bands. From these parameters it is concluded that in these glasses Mn 2+ occupies two sites, one octahedral and the other tetrahedral. This together with the conclusions drawn from the decay times, implies that the high energy band arises from tetrahedral manganese mainly in the Si-rich phase while the low energy emission is due to octahedrally coordinated manganese located primarily in the B-rich phase.
Chemical Physics Letters | 1983
J.G. Kang; T.F. Belliveau; David J. Simkin
Abstract We report here the observation and measurement of the temperature dependence of the slow component in the radiative decay of the A-band emission from KBr : Pb2+. The results of these measurements, together, with those reported on the fast components permit a complete analysis of the decay kinetics of the A-band emission. A model for the relaxed excited state which is consistent with analogous systems is presented.
Chemical Physics Letters | 1979
David J. Simkin; J.P. Martin; Le Si Dang; Yoshio Kamashina
Abstract An expression for the decay time as a function of an applied magnetic field is derived for the particular cases of A-band emission in KI: In + and KI: Sn 2+ . Application of this analysis to the measured field dependence gives the value of g ⊥ for the emitting level as well as the symmetry of the relaxed excited state.
Journal of The Optical Society of America B-optical Physics | 1996
Andrei G. Skirtach; David J. Simkin; Simon A. Boothroyd
We present the results of nondegenerate two-wave mixing measurements in Cr−3:YAlO3 and in Cr−3: Er−3:YAlO3 in which the induced index change arises from the population of the 2E excited state of the chromium. The presence of erbium ions alters the 2E-level lifetime and quenches the chromium nonlinearity. We interpret our results in terms of a model in which different lifetimes are assigned to the chromium ions. Chromium ions close enough to an erbium ion to experience quenching by nonradiative energy transfer have lifetimes that are shorter than chromium ions that are not affected by energy transfer.
Molecular Physics | 1979
Keiko Oyama Gannon; David J. Simkin; P.W.M. Jacobs; Martin J. Stillman
Measurements of the magnetic circular dichroism (MCD) in the A, B and C bands of KBr: In+ have been made over a wide temperature range 5 to ∼180 K. An analysis of the moments of these MCD spectra and of the absorption spectra of the same crystals, yields the values of the coupling constants to lattice modes of A 1g , Eg and T 2g symmetry for both the singlet and triplet T 1u states of the a 1g t 1u configuration. A knowledge of these parameters permits an ab initio calculation of the MCD line shape in the semiclassical approximation, the results of which are in generally good agreement with the experimental data. The temperature-dependence of the effective g-factor for the A band has been observed for the first time in such systems and an analysis of this provides an approximate value for g for the triplet state.
Optics Communications | 1982
G.P. Pazzi; M.G. Baldecchi; P. Fabeni; R. Linari; A. Ranfagni; M. Cetica; David J. Simkin
Abstract In order to verify the possibility of obtaining laser action in doped alkali-halides crystals, optical amplification measurements have been performed by the amplified spontaneous emission (ASE) technique. Results obtained in CsI : In(Tl) crystal are reported and discussed.
Journal of Luminescence | 1981
David J. Simkin; Keiko Oyama-Gannon; Pierre Menassa; Peter Taylor
Abstract Evidence is presented that the luminescent decay times of Mn 2+ activators can be used as a probe to signal the onset of thermal phase separation of sodium borosilicate glasses.
Journal of Chemical Physics | 1971
J. P. Larkindale; David J. Simkin
Carbon‐13 chemical‐shift data on pyridine and its charge‐transfer complex with iodine are presented. The Karplus‐Pople theory of chemical shifts, together with CNDO/2‐SCF MO calculations, is found to lead to good semiquantitative agreement with experiment. It is shown that both bond orders and electron density must be taken into account to obtain agreement with experiment. Carbon‐13 shift measurements, like proton shift measurements, do not enable the amount of charge transfer to be estimated. Under the experimental conditions used, no estimate of the equilibrium constant could be obtained, but the shifts of the carbon atoms in the pure complex were estimated.
Chemical Physics Letters | 1991
M. Laberge; David J. Simkin; Bruce S. Dunn
Abstract The introduction of trivalent europium and samarium into β″-alumina yields materials in which energy transfer can be observed, either between europium ions in the Eu 3+ -doped crystal or between samarium and europium in the Co-doped species. We have identified an acceptor site in europium by monitoring its 5 D 0 → 7 F 2 emission, where two of the europium crystallographic sites can be distinguished. In the europium-doped species, energy is preferentially accepted by the 608.1 nm component of a Beevers—Ross site at 300 K but not at 77 K. In the EuSm Co-doped species, samarium to europium transfer is observed at both 300 and 77 K.