32 research outputs found
External Electric Field Effect on Fluorescence Spectra of Pyrene in Solution
Electrophotoluminescence
(E-PL) spectra, i.e., plots of the electric-field-induced change in
photoluminescence intensity as a function of wavenumber, have been
measured for pyrene solution. At high concentrations of pyrene where
excimer fluorescence is observed along with the monomer fluorescence
emitted from the locally excited state, both excimer fluorescence
and monomer fluorescence are enhanced by application of electric fields.
The results show that the nonradiative decay process at the excimer
emitting state is decelerated by application of electric fields. It
is also found that molecular polarizability of pyrene excimer is larger
than that of pyrene monomer in the ground state by ∼270 ±
90 Ã…<sup>3</sup>, based on the analysis of the Stark shift of
the excimer fluorescence
Insulator–Metal Transitions Induced by Electric Field and Photoirradiation in Organic Mott Insulator Deuterated κ-(BEDT-TTF)<sub>2</sub>Cu[N(CN)<sub>2</sub>]Br
The Mott insulator–metal transition induced by
an external
stimulus such as electric field, pressure, chemical doping, or photoirradiation
has received considerable attention because of the potential use in
new optoelectronic functional devices. Here we report an abrupt Mott
insulator–metal transition observed as a current jump in a
molecular-based Mott insulator, namely, deuterated κ-(BEDT-TTF)2CuÂ[NÂ(CN)2]ÂBr, where BEDT-TTF = bisÂ(ethylenedithio)Âtetrathiafulvalene,
upon application of a pulsed voltage of certain magnitude (threshold
voltage). Furthermore, the threshold voltage needed for the transition
is shown to be reduced by photoirradiation. Thus, the Mott insulator–metal
transition can be controlled by a combination of an external electric
field and photoirradiation
Electroabsorption Spectra of Quantum Dots of PbS and Analysis by the Integral Method
Electroabsorption (E-A) spectra of
semiconductor quantum dots (QDs)
of PbS have been analyzed by the integral method, which is powerful
not only to determine the change in electric dipole moment and/or
polarizability following absorption precisely but also to confirm
the weak absorption bands buried under other strong absorption bands.
In the results, two weak absorption bands which induce blue-shift
and red-shift, respectively, with application of electric fields have
been newly confirmed in PbS QDs to be located just above the intense
first exciton band. The energy separation between these two bands
becomes smaller, as the applied field strength becomes stronger, suggesting
that the interaction between the states excited by these transitions
becomes weaker by application of electric fields. The QD size dependence
has been reported both for the transition energy and for the magnitude
of the change in electric dipole moment and molecular polarizability
following the absorption of each band. The assignment of the absorption
bands has also been discussed
A Memory Effect Controlled by a Pulsed Voltage in Photoinduced Conductivity Switching in an Organic Charge-Transfer Salt
We report that the photoinduced high conductivity (HC) state in the organic charge-transfer salt α-(BEDT-TTF)2I3, which is initially triggered by a pulsed voltage and synchronous photoirradiation, can be repeatedly recovered without further photoirradiation by application of a pulsed voltage even after the current has been reduced to zero. The recovery to the HC state can be controlled by adjusting the pulse width and/or amplitude. By proper selection of pulsed voltage parameters, the switching can be made reversible or irreversible. Hysteresis loops in the current−voltage and current−irradiation intensity curves of the circuit demonstrate a memory effect with potential application in unconventional photoswitching operations. The characteristic of the hysteresis loop and current bistability can be flexibly varied by changing the width of the applied pulsed voltage
Insulator–Metal Transitions Induced by Electric Field and Photoirradiation in Organic Mott Insulator Deuterated κ-(BEDT-TTF)<sub>2</sub>Cu[N(CN)<sub>2</sub>]Br
The Mott insulator–metal transition induced by
an external
stimulus such as electric field, pressure, chemical doping, or photoirradiation
has received considerable attention because of the potential use in
new optoelectronic functional devices. Here we report an abrupt Mott
insulator–metal transition observed as a current jump in a
molecular-based Mott insulator, namely, deuterated κ-(BEDT-TTF)<sub>2</sub>CuÂ[NÂ(CN)<sub>2</sub>]ÂBr, where BEDT-TTF = bisÂ(ethylenedithio)Âtetrathiafulvalene,
upon application of a pulsed voltage of certain magnitude (threshold
voltage). Furthermore, the threshold voltage needed for the transition
is shown to be reduced by photoirradiation. Thus, the Mott insulator–metal
transition can be controlled by a combination of an external electric
field and photoirradiation
Synergy Effects of Electric and Magnetic Fields on Locally Excited-State Fluorescence of Photoinduced Electron Transfer Systems in a Polymer Film
Photoluminescence of electron donor−acceptor pairs that show photoinduced electron transfer (PIET) has been measured in a polymer film under simultaneous application of electric field and magnetic field. Fluorescence emitted from the locally excited state (LE fluorescence) of 9-methylanthracene (MAnt) and pyrene (Py) is quenched by an electric field in a mixture of 1,3-dicyanobenzene (DCB) with MAnt or Py, indicating that PIET from the excited state of MAnt or Py to DCB is enhanced by an electric field. Simultaneous application of electric and magnetic fields enhances the reverse process from the radical-ion pair produced by PIET to the LE fluorescent state of MAnt or Py. As a result, the electric-field-induced quenching of the LE fluorescence is reduced by application of the magnetic fields. Thus, the synergy effect of electric and magnetic fields is observed on the LE fluorescence of MAnt or Py. Exciplex fluorescence spectra resulting from PIET can be obtained by analyzing the field effects on photoluminescence spectra, even when the exciplex fluorescence is too weak to be determined from the steady-state or time-resolved photoluminescence spectra at zero field
Stark Spectroscopy of Rubrene. II. Stark Fluorescence Spectroscopy and Fluorescence Quenching Induced by an External Electric Field
We
report Stark fluorescence spectroscopy investigation of rubrene
dispersed in a polyÂ(methyl methacrylate) film. The features of the
fluorescence spectrum are analogous to those in solutions. In the
Stark fluorescence spectrum, the decrease of the fluorescence quantum
yield in the presence of an external electric field is observed. This
result shows that the yield of nonradiative decay processes is increased
by the application of an external electric field. It is known that
the fluorescence quantum yield for rubrene, which is nearly unity
at room temperature, depends on temperature, and a major nonradiative
decay process in photoexcited rubrene is ascribed to a thermally activated
intersystem crossing (ISC). Equations that express the field-induced
fluorescence quenching in terms of the molecular parameters are derived
from the ensemble average of electric field effects on the activation
energy of the reaction rate constant in random orientation systems.
The molecular parameters are then extracted from the observed data.
It is inferred that the field-induced increase in the yield of other
intramolecular and intermolecular photophysical processes in addition
to the ISC should be taken into account
Effects of Nanosecond Pulsed Electric Fields on the Intracellular Function of HeLa Cells As Revealed by NADH Autofluorescence Microscopy
The fluorescence
lifetime of the endogenous fluorophore of reduced
nicotinamide adenine dinucleotide (NADH) in HeLa cells is affected
by the application of nanosecond pulsed electric fields (nsPEFs).
In this study, we found that after nsPEF application, the fluorescence
lifetime became longer and then decreased in a stepwise manner upon
further application, irrespective of the pulse width in the range
of 10–50 ns. This application time dependence of the NADH fluorescence
lifetime is very similar to the time-lapse dependence of the NADH
fluorescence lifetime following the addition of an apoptosis inducer,
staurosporine. These results, as well as the membrane swelling and
blebbing after the application of nsPEFs, indicate that apoptosis
is also induced by the application of nsPEFs in HeLa cells. In contrast
to the lifetime, the fluorescence intensity remarkably depended on
the pulse width of the applied nsPEF. When the pulse width was as
large as 50 ns, the intensity monotonically increased and was distributed
over the entire cell as the application duration became longer. As
the pulse width of the applied electric field became smaller, the
magnitude of the field-induced increase in NADH fluorescence intensity
decreased; the intensity was reduced by the electric field when the
pulse width was as small as 10 ns. These results suggest that the
mechanism of electric-field-induced apoptosis depends on the pulse
width of the applied nsPEF
Insulator–Metal Transitions Induced by Electric Field and Photoirradiation in Organic Mott Insulator Deuterated κ-(BEDT-TTF)<sub>2</sub>Cu[N(CN)<sub>2</sub>]Br
The Mott insulator–metal transition induced by
an external
stimulus such as electric field, pressure, chemical doping, or photoirradiation
has received considerable attention because of the potential use in
new optoelectronic functional devices. Here we report an abrupt Mott
insulator–metal transition observed as a current jump in a
molecular-based Mott insulator, namely, deuterated κ-(BEDT-TTF)<sub>2</sub>CuÂ[NÂ(CN)<sub>2</sub>]ÂBr, where BEDT-TTF = bisÂ(ethylenedithio)Âtetrathiafulvalene,
upon application of a pulsed voltage of certain magnitude (threshold
voltage). Furthermore, the threshold voltage needed for the transition
is shown to be reduced by photoirradiation. Thus, the Mott insulator–metal
transition can be controlled by a combination of an external electric
field and photoirradiation
Integral Method Analysis of Electroabsorption Spectra and Its Application to Quantum Dots of PbSe
The
integral method is proposed to analyze the electroabsorption (E-A)
spectra, since the change in the electric dipole moment and/or polarizability
following absorption can be determined precisely and the bands buried
under strong absorption bands can be confirmed. This method, where
not only the observed E-A spectra but also each of their first and
second integral spectra are fitted using the absorption and their
derivative and integral spectra, has been successfully applied to
the E-A spectra of semiconductor quantum dots of PbSe. In the results,
one absorption band, which is not identified in the absorption spectrum
because of the extremely weak intensity and also showing a remarkable
blue shift in the presence of an electric field because of the large
difference in polarizability between the ground state and the excited
state, has been confirmed to be located between the first and second
strong exciton bands. The size dependence of PbSe QDs of the peak
position of the newly confirmed band as well as the magnitude of the
change in electric dipole moment and polarizability following the
absorption of each absorption band is also reported, based on the
analysis by the integral method