43 research outputs found
Spatially, Temporally and Polarization-Resolved Photoluminescence Exploration of Excitons in Crystalline Phthalocyanine Thin Films
The lack of long range order in organic semiconductor thin films prevents the
unveiling of the complete nature of excitons in optical experiments, because
the diffraction limited beam diameters in the bandgap region far exceed typical
crystalline grain sizes. Here we present spatially-, temporally- and
polarization-resolved dual photoluminescence/linear dichroism microscopy
experiments that investigate exciton states within a single crystalline grain
in solution-processed phthalocyanine thin films. These experiments reveal the
existence of a delocalized singlet exciton, polarized along the high mobility
axis in this quasi-1D electronic system. The strong delocalized {\pi} orbitals
overlap controlled by the molecular stacking along the high mobility axis is
responsible for breaking the radiative recombination selection rules. Using our
linear dichroism scanning microscopy setup we further established a rotation of
molecules (i.e. a structural phase transition) that occurs above 100 K prevents
the observation of this exciton at room temperature.Comment: submitted to Journal of Chem Phys letter
The Sudbury Neutrino Observatory
The Sudbury Neutrino Observatory is a second generation water Cherenkov
detector designed to determine whether the currently observed solar neutrino
deficit is a result of neutrino oscillations. The detector is unique in its use
of D2O as a detection medium, permitting it to make a solar model-independent
test of the neutrino oscillation hypothesis by comparison of the charged- and
neutral-current interaction rates. In this paper the physical properties,
construction, and preliminary operation of the Sudbury Neutrino Observatory are
described. Data and predicted operating parameters are provided whenever
possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and
epsf style files. For additional information about SNO see
http://www.sno.phy.queensu.ca . This version has some new reference
Electronic and optical properties of magnesium phthalocyanine (MgPc) solid films studied by soft X-ray excited optical luminescence and X-ray absorption spectroscopies
In a study to link the optical and structural properties of solid films of magnesium Phthalocyanine (MgPc), a range of synchrotron based spectroscopic methods have been used. These include X-ray excited optical luminescence (XEOL) together with X-ray absorption spectroscopy (XAS) measured both by total electron yield methods (TEY) and by using the optically detected photoluminescence yield method (PLY). XEOL spectra below K shell threshold show a broad emission peak at ~860 nm which can be attributed to the optical Q band of these organic systems, which is then suppressed above the threshold. The shift to higher wavelength compared to optical emission spectra from MgPc in solution is consistent with intermolecular coupling of the excited states in the loosely intermolecular bonded phthalocyanine crystal structure. Zero order total PLY spectra at both C and N K edges are compared to TEY spectra where at the C K edge an inversion of intensity ratios between features is observed. Wavelength-specific PLY absorption spectra taken at 860 nm at the N K edge show a role for 蟽* states participating in the luminescence process possibly through the 蟽-like lone pair of bridging nitrogen atom, denoted the n卢蟺* transition