Erick Piovesan

Resonant Nonlinear Absorption in Zn-Phthalocyanines

In this work, we investigate the nonlinear absorption dynamics of Zn phthalocyanine in dimethyl sulfoxide (DMSO). We used single pulse and pulse train Z-scan techniques to determine the dynamics and absorption cross-sections of singlet and triplet states at 532 nm. The excited singlet state absorption cross-section was determined to be 3.2 times higher than the ground state one, giving rise to reverse saturable absorption. We also observed that reverse saturable absorption occurs from the triplet state, after its population by intersystem crossing, whose characteristic time was determined to be 8.9 ns. The triplet state absorption cross-section determined is 2.6 times higher than the ground state one. In addition, we used the white light continuum Z-scan to evaluate the singlet excited state spectrum from 450 to 710 nm. The results show two well-defined regions, one above 600 nm, where reverse saturable absorption is predominant. Below 600 nm, we detected a strong saturable absorption. A three-energy-level diagram was used to explain the experimental results, leading to the excited state absorption cross-section determination from 450 nm up to 710 nm.

Broadband three-photon absorption spectra of platinum acetylide complexes

We investigate the three-photon absorption spectra of four platinum acetylides complexes employing femtosecond pulses. We observed strong three-photon absorption cross-section in the near-infrared region (from 850 nm to 1200 nm). The three-photon absorption (3PA) spectra present resonance enhancement effect as two photons of the excitation wavelength approach the lower two-photon allowed states of the molecules as well as a 3PA allowed band around 1180 nm. The 3PA cross-section spectra were interpreted using the sum-over-essential-states approach, considering a three-energy-level diagram.

Enhanced optical and electrical properties of layer-by-layer luminescent films

The electrical and optical properties of luminescent films from poly(p-phenylene vinylene) (PPV) and poly(o-methoxyaniline) (POMA) produced via the layer-by-layer technique are reported. POMA layers were obtained in a nonself-limiting process from its emeraldine salt. PPV was thermally converted from the precursor poly(xylylidene tetrahydrothiophenium chloride) with sodium dodecylbenzenesulfonate (DBS) at low temperatures of ∼110 °C and short times (∼30 min). The line shape of absorbance and photoluminescence (PL) is not affected with the PPV conversion reaction. High thermal stability of PPV was observed, with the integrated PL decreasing only 10% when the temperature was increased from 10 to 300 K. This decrease was accompanied by a small blue shift of 5 nm in the zero-phonon peak and a low electron–phonon coupling with a Huang–Rhys factor S<1 in the vibration spectral region. The combination of POMA and indium–tin–oxide (ITO) as transparent electrode and PPV+DBS as active layer (ITO/POMA/PPV+DBS/Al) le...

Substrate/semiconductor interface effects on the emission efficiency of luminescent polymers

The importance of interface effects for organic devices has long been recognized, but getting detailed knowledge of the extent of such effects remains a major challenge because of the difficulty in distinguishing from bulk effects. This paper addresses the interface effects on the emission efficiency of poly(p-phenylene vinylene) (PPV), by producing layer-by-layer (LBL) films of PPV alternated with dodecylbenzenesulfonate. Films with thickness varying from ∼15 to 225 nm had the structural defects controlled empirically by converting the films at two temperatures, 110 and 230 °C, while the optical properties were characterized by using optical absorption, photoluminescence (PL), and photoluminescence excitation spectra. Blueshifts in the absorption and PL spectra for LBL films with less than 25 bilayers (<40–50 nm) pointed to a larger number of PPV segments with low conjugation degree, regardless of the conversion temperature. For these thin films, the mean free-path for diffusion of photoexcited carriers ...

Structure control of poly(p-phenylene vinylene) in layer-by-layer films by deposition on a charged poly(o-methoxyaniline) cushion

In this paper, we demonstrate that the intrinsic electric field created by a poly(o-methoxyaniline) (POMA) cushion layer hinders the changes in molecular conformation of poly(p-phenylenevinylene) (PPV) in layer-by-layer with dodecylbenzene sulfonic acid (DBS). This was modeled with density functional theory (DFT) calculations where an energy barrier hampered molecular movements of PPV segments when they were subjected to an electric field comparable to that caused by a charged POMA layer. With restricted changes in molecular conformation, the PPV film exhibited Franck-Condon transitions and the photoexcitation spectra resembled the absorption spectra, in contrast to PPV/DBS films deposited directly on glass, with no POMA cushion. Other effects from the POMA cushion were the reduced number of structural defects, confirmed with Raman spectroscopy, and an enhanced PPV emission at high temperatures (300 K) in comparison with the films on bare glass. The positive effects from the POMA cushion may be exploited ...

Nonlinear Optical Properties of Phenyl Diphenylamine Derivatives and Platinum Acetylide Complexes

This work presents a study on the nonlinear optical properties of organic and organometallic compounds, using femtosecond Z-Scan. Results show reasonable two-photon absorption cross-section, which make these compounds good candidates for technological applications.