13 research outputs found
Vis and NIR Diffuse Reflectance Study in Disordered Bismuth Manganate - Lead Titanate Ceramics
This work shows a correlation between light reflectance, absorption, and morphologies of
series of bismuth manganate–lead titanate, (1 x) BM–x PT, (x = 0.00, 0.02, 0.04, 0.08, 0.12, 0.16, 0.24,
1.00) ceramics composite. Low reflectance in the Vis-NIR range corresponds to ‘black mirror’ features.
The modified Kubelka-Munk function applied to measured visible-near infrared (Vis-NIR) diffuse
reflectance enabled the estimation of the energy gaps magnitude of the order of 1.0–1.2 eV for BM-PT.
Histograms of grains, obtained using a scanning electron microscope, enabled finding the correlation
between grains size, reflectance magnitude, and PT content. The magnitude of energy gaps was
attributed to electronic structure bands modified by crystal lattice disorder and oxygen vacancies
Fingerprints of Through-Bond and Through-Space Exciton and Charge π-Electron Delocalization in Linearly Extended [2.2]Paracyclophanes
New stilbenoid and
thiophenic compounds terminally functionalized
with donor–donor, acceptor–acceptor, or donor–acceptor
moieties and possessing a central [2.2]paracyclophane unit have been
prepared, and their properties interpreted in terms of through-bond
and through space π-electron delocalization (i.e., π-conjugations).
Based on photophysical data, their excited-state properties have been
described with a focus on the participation of the central [2.2]paracyclophane
in competition with through-bond conjugation in the side arms. To
this end, two-photon and one-photon absorption and emission spectroscopy,
as a function of temperature, solvent polarity, and pressure in the
solid state have been recorded. Furthermore, charge delocalization
through the [2.2]paracyclophane in the neutral state and in the oxidized
species (radical cations, dications and radical trications) has been
investigated, allowing the elucidation of the vibrational Raman fingerprint
of through-space charge delocalization. Thus, a complementary approach
to both “intermolecular” excitation and charge delocalizations
in [2.2]paracyclophane molecules is shown which can serve as models
of charge and exciton migration in organic semiconductors
The Two-Photon Absorption Cross-Section Studies of CsPbX3 (X = I, Br, Cl) Nanocrystals
The CsPbX3 nanocrystals (NCs) with X = I, Br, Cl, or the mixture of Br:I and Br:Cl in a 1:1 ratio were synthesized and characterized by TEM, DLS, and XRD. Recrystallization of the small luminescent NCs in the metastable cubic phase into bigger orthorhombic nanocrystals was monitored by XRD and identified as the main cause of the nanocolloid coagulation. The recrystallization also leads to a decrease in the photoluminescence quantum yield (QY) of the colloidal solution and shortening of the emission lifetime. The two-photon absorption cross-section σ2 values calculated from femtosecond Z-scan measurements were compared with those obtained based on the two-photon excited emission technique. These two techniques were shown to be equivalent with the cross-section values calculated per molar mass of CsPbX3 perovskite being in the range of 10–200 GM depending on the halide anions X−. The σ2 values recalculated for the mole of the NCs were in the range of 104–105 GM, which is in good agreement with values previously reported elsewhere and the σ2/M parameter was in the range of 0.01 to 0.33. This study shows the perovskite NCs to be a good nonlinear material with the third-order nonlinear optical susceptibility χ(3) of the NCs on the order of 10−11 esu
Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission
Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation. The most significant value of two-photon absorption cross section σ2 for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ2Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for nonlinear bioimaging
Porous anodic alumina formed by anodization of aluminum alloy (AA1050) and high purity aluminum
Third-Order Nonlinear Optical Properties of Infrared Emitting PbS and PbSe Quantum Dots
The
optical properties of small band gap, colloidal quantum dots
are presented, with the special emphasis put on the measurements of
their nonlinear optical properties in the infrared region of spectra.
In particular, two types of colloidal quantum dots (PbS and PbSe),
with the first exciton absorption band maxima in the near-infrared
region of spectra, were investigated using a tunable femtosecond laser
system and the <i>Z</i>-scan technique. The measurements
of closed- and open-aperture <i>Z</i>-scan traces allowed
for the calculation of real and imaginary parts of cubic nonlinearity,
which were presented as appropriate cross sections used to characterize
the nonlinear refractive and absorptive properties of the studied
quantum dots. The maximum two-photon absorption cross section values
taken for a single quantum dot were found to be ∼2400 GM (Goeppert-Mayer
units) at 1300 nm and ∼15 500 GM at 1700 nm, for PbS
and PbSe QDs, respectively. PbS quantum dots showed two-photon induced
emission upon infrared excitation. The obtained results demonstrate
the potential of IV–VI group colloidal quantum dots for low-cost
photonic devices and two-photon absorbers in the near-infrared and
infrared spectral ranges
Enhancement of Two-Photon Absorption Cross Section in CdSe Quantum Rods
Nonlinear optical properties of semiconducting
CdSe quantum rods
(QRs), with three various aspect ratios, were examined in a wide wavelength
range using femtosecond Z-scan technique. The two-photon absorption
cross section σ<sub>2</sub> was found to be as large as 164 000
GM at the wavelength of 750 nm: about 4 times larger than that expected
for CdSe quantum dots of the same mass. On the basis of the obtained
dispersion of the two-photon absorption cross section, we have selected
wavelength ranges for optimal excitation of two-photon-induced emission.
We have also studied the luminescence kinetics using degenerate pump–probe
and time-correlated single-photon counting techniques. A strong influence
of semiconducting CdSe rods morphology on their steady-state and time-resolved
optical properties was found
Wavelength Dependence of the Complex Third-Order Nonlinear Optical Susceptibility of Poly(3-hexylthiophene) Studied by Femtosecond <i>Z</i>‑Scan in Solution and Thin Film
Comprehensive studies of the third-order
susceptibility of regioregular
poly(3-hexylthiophene) in the wavelength range from 530 to 1600 nm
for both thin film (with stacked chains interactions) and dilute solution
(no chains interactions) were performed with the <i>Z</i>-scan technique. Negative nonlinear refraction was observed in the
whole wavelength range of the measurements. The nonlinear absorption
exhibits regions of two-photon and three-photon absorption, and on
approaching the linear absorption region, a saturable absorption process
is seen. It was found that for thin film the effective multiphoton
absorption cross-sections σ<sub>2</sub> and σ<sub>3</sub> are 1.5 and 3 times bigger than for solution, respectively. Influence
of the elongated conjugation length in the stacked polythiophene chains
in thin film on the red shift of the multiphoton absorption cross-section
spectra in comparison with those for polythiophene in solution is
discussed
Synthesis and Linear and Nonlinear Optical Properties of Three Push–Pull Oxazol-5(4<i>H</i>)‑one Compounds
Three
uncharged push–pull oxazol-5(4<i>H</i>)-ones
were synthesized and thoroughly characterized. The examined molecules
contained electron-donor and electron-acceptor groups interacting
via a π-conjugated bridge. Spectral properties of the oxazol-5(4<i>H</i>)-ones were studied in detail in three solvents of different
polarities. The results indicate a solvatochromic shift toward lower
energy for the charge-transfer state. The compounds are weakly fluorescent
in polar solvents, but they have high fluorescence quantum yields
in nonpolar solvents. Their two-photon absorption (2PA) properties
were characterized by the open- and closed-aperture Z-scan technique,
by the pump–probe technique, and by the two-photon excited
fluorescence method. The dyes exhibit relatively high effective two-photon
absorption cross sections ranging from 490 to 2600 GM at ∼100
GW/cm<sup>2</sup>, according to the Z-scan results, which are found,
however, to contain significant contribution from higher-order absorption
processes. In addition, these compounds display good photostability