" Studies on Laser induced Phatothermal Phenomena in Selected Organic Compounds and Fullerenes"

In the pre—laser era it was difficult to believe that the optical properties of a medium depend upon the intensity of the radiation incident on it. The basis for this conclusion is that the electric field strength associated with the conventional light sources used before the advent of lasers was much smaller than (103 V/cm) the field sttrengths of atomic or interatomic fields (2 107 —- 10” V/cm). The radiation with such low intensity is not able to affect atomic fields to the extent of changing optical parameters. The invention of laser in 1960 was a turning point. The high degree of coherence of the laser radiation provides high spatial concentration of optical power. With the availability of the femtosecond lasers it has become possible to get extremely high peak powers 2 1013 W/cmz). At such high fields, the relationship between electric ‘polarization P and the electric field strength E ceases to be linear and several nonlinear effects begin to occur. Nonlinear absorption, a branch of nonlinear optics, refers to the interaction between radiation and matter accompanied by absorption of more than one photon. Nonlinear absorption has acquired great importance after the invention of high power lasers. One of the objectives of the present work is to investigate the nonlinear absorption processes occurring in fullerene, selected organic solvents and laser dyes. Fullerenes and laser dyes were chosen because of their highly nonlinear behaviour. Fullerenes, the most beautiful among molecules, offer fascinating field of research owinglto their significant structural properties. As toluene, benzene and carbon disulphide are themost widely used solvents for fullerenes, it seems important to study the nonlinear properties of these liquids as well. Like fullerenes, laser dyes also possess highly delocalized 7r electrons which are responsible for their nonlinear absorption. Dye lasers were the fulfillment of an experimenter’s pipe dream - to have a laser that is easily tunable over a wide range of wavelengths. A better understandingof the photophysical properties of laser dyes can significantly enhance the development and technology of dye lasers. We studied the nonlinear absorption properties of two rhodamine dyes to have some insight into their nonlinear optical properties.

Thermo- Optic and Nonlinear-Optical studies on CdSe Quantum Dots for Photonic Applications

In general, linear- optic, thermo- optic and nonlinear- optical studies on CdSe QDs based nano uids and their special applications in solar cells and random lasers have been studied in this thesis. Photo acous- tic and thermal lens studies are the two characterization methods used for thermo- optic studies whereas Z- scan method is used for nonlinear- optical charecterization. In all these cases we have selected CdSe QDs based nano uid as potential photonic material and studied the e ect of metal NPs on its properties. Linear optical studies on these materials have been done using vari- ous characterization methods and photo induced studies is one of them. Thermal lens studies on these materials give information about heat transport properties of these materials and their suitability for applica- tions such as coolant and insulators. Photo acoustic studies shows the e ect of light on the absorption energy levels of the materials. We have also observed that these materials can be used as optical limiters in the eld of nonlinear optics. Special applications of these materials have been studied in the eld of solar cell such as QDSSCs, where CdSe QDs act as the sensitizing materials for light harvesting. Random lasers have many applications in the eld of laser technology, in which CdSe QDs act as scattering media for the gain.

Continuous and gradual photo-activation methods: influence on degree of conversion and crosslink density of composite resins

Thermal properties and degree of conversion (DC%) of two composite resins (microhybrid and nanocomposite) and two photo-activation methods (continuous and gradual) displayed by the light-emitting diode (LED) light-curing units (LCUs) were investigated in this study. Differential scanning calorimetry (DSC) thermal analysis technique was used to investigate the glass transition temperature (T(g)) and degradation temperature. The DC% was determined by Fourier transform infrared spectroscopy (FT-IR). The results showed that the microhybrid composite resin presented the highest T(g) and degradation temperature values, i.e., the best thermal stability. Gradual photo-activation methods showed higher or similar T(g) and degradation temperature values when compared to continuous method. The Elipar Freelight 2 (TM) LCU showed the lowest T(g) values. With respect to the DC%, the photo-activation method did not influence the final conversion of composite resins. However, Elipar Freelight 2 (TM) LCU and microhybrid resin showed the lowest DC% values. Thus, the presented results suggest that gradual method photo-activation with LED LCUs provides adequate degree of conversion without promoting changes in the polymer chain of composite resins. However, the thermal properties and final conversion of composite resins can be influenced by the kind of composite resin and LCU.

Study on the observation of Eu(2+) and Eu(3+) valence states in low silica calcium aluminosilicate glasses

The optical, magnetic and structural properties of Eu doped low silica calcium aluminosilicate glasses were investigated. The optical absorption coefficient presented two bands at 39 246 and 29 416 cm(-1), which were assigned respectively to the 4f(7) ((8)S(7/2)) -> 4f(6) (4F(J)) 5d (T(2g)), and 4f(7) ((8)S(7/2)) -> 4f(6) (4F(J)) 5d (E(g)) transitions of Eu(2+). The fluorescence measured at 300 K on a sample doped with 0.5 wt% of Eu(2)O(3) exhibited a broad band centered at 17 350 cm(-1), which is attributed to the 4f(6)5d -> 4f(7) transition of Eu(2+), whereas the additional peaks are due to the (5)D(0) -> (7)F(J) (J = 1, 2, 4) transitions of Eu(3+). From magnetization and XANES data it was possible to evaluate the fractions of Eu(2+) and Eu(3+) for the sample doped with 0.5 and 5.0 wt% of Eu(2)O(3), the values of which were approximately 30 and 70%, respectively.

Physical Vapor Deposited Thin Films of Lignins Extracted from Sugar Cane Bagasse: Morphology, Electrical Properties, and Sensing Applications

The concern related to the environmental degradation and to the exhaustion of natural resources has induced the research on biodegradable materials obtained from renewable sources, which involves fundamental properties and general application. In this context, we have fabricated thin films of lignins, which were extracted from sugar cane bagasse via modified organosolv process using ethanol as organic solvent. The films were made using the vacuum thermal evaporation technique (PVD, physical vapor deposition) grown up to 120 nm. The main objective was to explore basic properties such as electrical and surface morphology and the sensing performance of these lignins as transducers. The PVD film growth was monitored via ultraviolet-visible (UV-vis) absorption spectroscopy and quartz crystal microbalance, revealing a linear relationship between absorbance and film thickness. The 120 nm lignin PVD film morphology presented small aggregates spread all over the film surface on the nanometer scale (atomic force microscopy, AFM) and homogeneous on the micrometer scale (optical microscopy). The PVD films were deposited onto Au interdigitated electrode (IDE) for both electrical characterization and sensing experiments. In the case of electrical characterization, current versus voltage (I vs V) dc measurements were carried out for the Au IDE coated with 120 nm lignin PVD film, leading to a conductivity of 3.6 x 10(-10) S/m. Using impedance spectroscopy, also for the Au IDE coated with the 120 nm lignin PVD film, dielectric constant of 8.0, tan delta of 3.9 x 10(-3)) and conductivity of 1.75 x 10(-9) S/m were calculated at 1 kHz. As a proof-of-principle, the application of these lignins as transducers in sensing devices was monitored by both impedance spectroscopy (capacitance vs frequency) and I versus time dc measurements toward aniline vapor (saturated atmosphere). The electrical responses showed that the sensing units are sensible to aniline vapor with the process being reversible. AFM images conducted directly onto the sensing units (Au IDE coated with 120 nm lignin PVD film) before and after the sensing experiments showed a decrease in the PVD film roughness from 5.8 to 3.2 nm after exposing to aniline.

Pirólise de borras oleosas de petroleo utilizando nanomateriais

The oily sludge is a complex mix of hydrocarbons, organic impurities, inorganic and water. One of the major problems currently found in petroleum industry is management (packaging, storage, transport and fate) of waste. The nanomaterials (catalysts) mesoporous and microporous are considered promising for refining and adsorbents process for environment protection. The aim of this work was to study the oily sludge from primary processing (raw and treated) and vacuum residue, with application of thermal analyses technique (pyrolysis), thermal and catalytic pyrolysis with nanomaterials, aiming at production petroleum derived. The sludge and vacuum residue were analyzed using a soxhlet extraction system, elemental analysis, thin layer chromatography, thermogravimetry and pyrolysis coupled in gas chromatography/mass spectrometry (Py GC MS). The catalysts AlMCM-41, AlSBA-15.1 e AlSBA-15.2 were synthesized with molar ratio silicon aluminum of 50 (Si/Al = 50), using tetraethylorthosilicante as source of silicon and pseudobuhemita (AlOOH) as source of aluminum. The analyzes of the catalysts indicate that materials showed hexagonal structure and surface area (783,6 m2/g for AlMCM-41, 600 m2/g for AlSBA-15.1, 377 m2/g for AlSBA-15.2). The extracted oily sludge showed a range 65 to 95% for organic components (oil), 5 to 35% for inorganic components (salts and oxides) and compositions different of derivatives. The AlSBA-15 catalysts showed better performance in analyzes for production petroleum derived, 20% increase in production of kerosene and light gas oil. The energy potential of sludge was high and it can be used as fuel in other cargo processed in refinery

Physical Vapor Deposited Thin Films of Lignins Extracted from Sugar Cane Bagasse: Morphology, Electrical Properties, and Sensing Applications

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural and Electric-Optical Properties of Zinc Phthalocyanine Evaporated Thin Films: Temperature and Thickness Effects

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Inversion in the temperature coefficient of the optical path length close to the glass transition temperature in tellurite glasses

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Continuous and gradual photo-activation methods: influence on degree of conversion and crosslink density of composite resins

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

STUDY OF POLING BEHAVIOR OF BIAXIALLY STRETCHED POLY(VINYLIDENE FLUORIDE) FILMS USING THE CONSTANT-CURRENT CORONA TRIODE

This article reports systematic results of corona poling measurements obtained on biaxially stretched polyvinylidene fluoride films charged in dry air. Charging was performed using the constant current corona triode. The dependence of the poling process on the sample thickness, charging current, and successive charging processes was investigated. Phase transitions from alpha to delta and to beta phases were observed when virgin samples were corona charged. The thermal pulse technique showed that the polarization profiles during charging can be made consistently almost uniform and that the ferroelectric reorientation can be associated with the rising plateau region displayed on potential buildup curves. (C) 1995 American Institute of Physics.

Simple and versatile heterodyne whole-field interferometer for phase optics characterization

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Mechanism of the formation and properties of antimony polyphosphate

Formation of antimony polyphosphate using Sb2O3 and/or (NH4)2HPO4 and NH4H 2PO4 as starting materials has been simulated by thermal analysis technique. The elimination of water and ammonia molecules induced by heating leads to the formation of intermediate ammonium polyphosphate, which subsequently reacts with Sb2O3. Morphologically, vitreous Sb(PO3)3 is composed of plaques having irregular shapes. Infrared spectra and NMR study is consistent with tetrametaphosphate anion arrangement. The compound is thermally unstable and may be recommended as a donor of -O-P-O- linkers in the preparation of special phosphate glasses. © 2005 Akadémiai Kiadó, Budapest.

Síntese e caracterização de vidros teluritos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação óptica de vidros teluritos preparados com Er3+ e Er3+/Yb3+ para aplicação em fotônica

Pós-graduação em Ciência dos Materiais - FEIS