Thesis (Ph.D.)--Aerospace Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Seitzman, Jerry; Committee Member: Jagoda, Jechiel; Committee Member: Lieuwen, Tim; Committee Member: Menon, Suresh; Committee Member: Tan, David.

Como parte do principal programa do Laboratório de Cristais Iônicos do Departamento de Física Nuclear do Instituto de Física da Universidade de São Paulo, foi estudado no presente trabalho o mineral natural de cordierita, de fórmula química (Mg,Fe)(Al4Si5O18) . nH2O, amostra esta de Vana, oriunda da Bahia. O trabalho teve como enfoque as propriedades de termoluminescência (TL) e de ressonância paramagnética eletrônica (EPR). Foram obtidas curvas de emissão TL de uma amostra com dose adicional de 50 Gy no aparelho leitor montado no LACIFID, e outra de uma amostra com dose adicional de 2000 Gy no aparelho leitor do fabricante Daybreak Nuclear. As duas curvas apresentam um pico único aparente em torno de l50°C, estendendo-se de 50°C a 250°C. A curva de emissão TL da amostra com dose adicional de 2000 Gy apresentou um ombro muito pouco eminente entre 200\"C e250\"C, indicando a presença de outro pico nessa região. As amostras de cordierita com doses adicionais entre 50 Gy e 5000 Gy deram origem a curvas de emissão TL que mostram que deve haver um pico em torno de 100°C, instável à temperatura ambiente, e que quando é feita a leitura TL imediatamente após a irradiação das amostras, esse pico cresce muito rapidamente, dando a impressão de que o pico em 150°C deslocou-se para temperaturas menores. Na representação gráfica linear, a intensidade TL em função da dose é dada por uma curva exponencial do tipo I = I0[1 - exp (-D/DS)], onde I0 é a intensidade TL de saturação e DS a dose a partir da qual começa a saturação. No presente caso, para o pico TL em torno de 100°C, foram obtidos I0 ~- 4,6x105 em unidades arbitrárias, e Ds ~ 2000 Gy. Na escala logarítmica, obtém-se uma reta paralela à da linearidade, isto é, o pico TL em 100°C cresce linearmente com a dose. No entanto, o pico no intervalo 145°C 150°C apresenta supralinearidade; não muito acentuada, mas desde baixa dose (menos de 10 Gy), tornando-se sublinear em aproximadamente 800 Gy. O recozimento a uma temperatura de 600°C por uma hora antes da irradiação (no caso 500 Gy), provocou um aumento na sensibilidade do pico em 100°C, enquanto que com o recozimento a750°C por uma hora, a intensidade TL em 125°C é que sofreu aumento, e com o recozimento a 900°C por uma hora o que sofre aumento na intensidade é o pico no intervalo 145-150°C, de tal modo que dá a impressão de que o pico TL se desloca de 100°C para 150°C com o tratamento térmico de 600°C a 900°C por uma hora. O tratamento térmico isócrono a 72°C, 96°C, 116°C, 136°C, 150°C, 176°C, 196°C, 216°C, 228°C, 240°C, 260°C, 280°C e 300°C, mostrou que deve haver picos TL nos intervalos 130°C 140°C, 150°C 170°C, 210°C 220°C, 250°C 260°C e em 360°C. Com a deconvolução da curva de emissão, temos a confirmação desses picos. A determinação dos parâmetros E e s, relativos ao pico em torno de 145°C das curvas de emissão TL das Figuras VII-2 (a) e (b), foi feita usando o método de duas taxas de aquecimento, com o seguinte resultado: E = 1,305 eV e s = 3,569x1014 s-1. O método de E x Tstop desenvolvido por McKeever (1985), resultou, por outro lado, em vários patamares de energia, indicando vários picos nas regiões de 70-90°C, 95-105°C, 115-118°C, 132-138°C, 155-165°C, 175-195°C. O método de deconvolução da curva de emissão, introduzido por Gomez - Ros et al (1998), mostrou a existência de picos TL em 144°C (E = 0,98 eV; s = 1,715 x 1011 s-1), 178°C (E = 0,995 eV; s = 2,792x1010 s-1), 214°C (E = 1,13eV; s = 1,026 x 1011 s-10), 249°C (E = 1,15 eV; s = 2,323 x 1010 s-1) e 368°C (E = 1,19 eV; s = 2,824x108 s-1). O espectro de EPR da amostra natural apresentou: na região entre 2000 e 3600 Gauss, seis linhas características de Mn2+; em 1500 Gauss, a linha de Fe3+; e centrada em 3400 Gauss, a linha larga devido à interação dipolar de Fe3+. Outras linhas não foram identificadas. O tratamento térmico a 600°C por uma hora não fez se apresentarem novas linhas ou causou supressão de algumas, mas a linha de interação dipolar sofreu um aumento considerável, indicando que o tratamento térmico causou a transformação de Fe2+ em Fe3+, liberando elétrons. / The Ionic Crystals Laboratory at Physics Institute of the Sao Paulo University investigates, as its main research project, studies of physical properties of available natural Brazilian minerals of silicates. In the present work, thermoluminescense and electron paramagnetic resonance properties of cordierite, (Mg,Fe)(Al4Si5O18) . nH2O, from Vana, Bahia State have been investigated. Being natural mineral, a x-ray fluorescence analysis has been conducted, finding first of all 47 ,77 mol % of SiO2, 31,70 of Al2O3, 7,52 of MgO and 8,31 mol % of FeO, as basic component, of the cordierite crystal, and 0,287 mol% of MnO, 0,84 mol% of Na2O, 0,46 mol% CaO, 0,3 mol% K2O, 0,022mol% of TiO2 and several others in smaller concentration. Glow curves, one of a natural sample with 50 Gy additional -dose, registered in a indigenous TL reader and the other one of a natural sample irradiated to 2000 Gy additional dose obtained in Daybreak TL reader. Both glow curves are characterized by a very broad (from 50°C to 250°C) curve peaked at 150°C. The second glow curve, presents a light shoulder around 200 to 250°C. Anyway, in such a case, one expects more than two peaks composing that broad glow curve. The cordierite samples irradiated with different additional -doses in the range 50 - 5000 Gy, have originated TL glow curves that demonstrate the possible existence of a peak around 100°C, unstable in ambient temperature, but if it is read soon after irradiation, the glow curves show this peak increasing quickly, appearing that the peak around 150°C shifted itself toward smaller temperatures. In the linear representation, the TL intensity as function of the dose, is given by an exponential curve in the form I = I0[ - exp(-D/Ds)], where I0 is the TL saturation intensity and Ds is the dose of the beginning of the saturation. In the present case, I0 ~ 4,1 x 105 (arbitrary units) and Ds ~ 2000 Gy were obtained. In the logarithmic scale, it has been obtained a parallel to straight line of linearity for the 100°C TL peak. However, the peak TL around 145-150°C, presents supralinearity, not much pronounced, from low doses (below 10 Gy) up to 800 Gy; after that, becomes sublinear. The pre-irradiation annealing at 600°C/1h, has provoked an enhancement of sensibility of the 100°C peak; the pre-irradiation annealing at 750°C/1h has originated an enhancement of TL intensity of the 125°C peak; at 900°C/1h has originated an enhancement of TL intensity of the peak around 145-150°C; as consequence the TL peak seems to shift from 100°C to 150°C. The isochronous thermal treatment at 72°C, 96°C, 116°C, 136°C, 150°C, 176°C, 196°C, 216°C, 228°C, 240°C, 260°C, 280°C and 300°C, has shown the possible existence of TL peaks in the ranges 130°C 140°C, 150°C 170°C, 210°C 220°C, 250°C 260°C and at 360°C. The glow curve deconvolution calculation confirms the presence of these peaks. The determination of the parameters E and s, relative to peak around 145°C of the glow curves - Figures VII.2 (a) and (b) - was done by the method of two heating rates, and resulted: E ~ 1,305 eV and s ~ 3,569 x 1014 s-1. The E x Tstop method, developed by McKeever (1995), gives, on the other hand, several plateaus, indicating several peaks in the ranges 70-90°C, 95-105°C, 115-118°C, 132-138°C, 155-165°C, 175-195°C. E - values can be inferred from each plateau. The glow curve deconvolution, method developed by Gomez - Ros et al. (1998), has shown the existence of TL peaks at 144°C (E = 0,98 eV; s = 1,715 x 1011 s-1), 178°C (E = 0,995 eV; s = 2,792x1010 s-1), 214°C (E = 1,13eV; s = 1,026 x 1011 s-10), 249°C (E = 1,15 eV; s = 2,323 x 1010 s-1) e 368°C (E = 1,19 eV; s = 2,824x108 s-1). The EPR spectrum of the natural sample has presented in the interval of 3000 to 3600 Gauss 6 characteristic lines of Mn2+, the line of Fe3+ at 1500 Gauss and a broad line centered at 3400 Gauss owing to dipolar interaction of Fe3+. Other lines were not identified. The thermal treatment at 600°C/1h did not produce new EPR lines, neither suppressed other ones. On the other hand, the dipolar interaction line had a considerable increment, indicating that with the thermal treatment there happened the conversion from Fe2+ to Fe3+, releasing electrons, since the broad line around 3400 Gauss, due to dipolar interaction of Fe3+ - ions increased with this heat treatment.

Calculations were performed on transition-metal complexes to (1) extrapolate the structure and bonding of the ground and phosphorescent states (2) determine the luminescence energies and (3) assist in difficult assignment of luminescent transitions. In the [Pt(SCN)4]2- complex, calculations determined that the major excited-state distortion is derived from a b2g bending mode rather than from the a1g symmetric stretching mode previously reported in the literature. Tuning of excimer formation was explained in the [Au(SCN)2]22- by interactions with the counterion. Weak bonding interactions and luminescent transitions were explained by calculation of Hg dimers, excimers and exciplexes formed with noble gases.

Density functional (ca, BLYP, BPW91, B3LYP and B3PW91), MP2 and CCSD(T) methods in combination with LANL2DZ or cc-pVxZ-PP (where x=D(double), T(triple) Q(quadruple), and 5(quintuple)) basis sets have been employed in computing electronic transition energies of zinc and cadmium monomers. CCSD(T)/aug-cc-pV5Z-PP combination finds values that are 150 cm-1 from the experimental value for the zinc monomer and 240 cm-1 remove from the cadmium monomer excitation experimental value. These method/basis set combinations are also used to find spectroscopic values (re, De, we, wexe, Be , and Te) that rival experimental values for dimers and excimers. Examples of this can be seen with the CCSD(T)/aug-cc-pV5Z-PP combination phosphorescent emission results. The values found are within 120 cm-1 of the zinc emission energy and 290 cm-1 of the cadmium emission energy. While this combination rigorously models spectroscopic constants for monomers, dimers, and excimers, it does not efficiently model these constants for larger clusters with available modern computational resources. It is important to show spectroscopic trends (bonding, phosphorescent excitation and emissions) as clusters increase as the monomer and dimer emission energies do not model solid state metallophilic interactions and phosphorescence. The MP2/LANL2DZ combinations show qualitative cooperative bonding trends in group oligomers and extended excimers as size increases and shape change. Changes in excitation and emission energies are also shown as a function of size and shape of the clusters.

The major topics discussed are the phosphorescence sensitization in the lanthanides via energy transfer and in the organics by heavy atom effects. The f-f transitions in lanthanides are parity forbidden and have weak molar extinction coefficients. Upon complexation with the ligand, ttrpy (4'-p-Tolyl-[2,2':6',2"]-terpyridine) the absorption takes place through the ligand and the excitation is transferred to the lanthanides, which in turn emit. This process is known as "sensitized luminescence." Bright red emission from europium and bright green emission from terbium complexes were observed. There is ongoing work on the making of OLEDs with neutral complexes of lanthanide hexafluoroacetyl acetonate/ttrpy, studied in this dissertation. Attempts to observe analogous energy transfer from the inorganic donor complexes of Au(I) thiocyanates were unsuccessful due to poor overlap of the emissions of these systems with the absorptions of Eu(III) and Tb(III). Photophysics of silver-aromatic complexes deals with the enhancement of phosphorescence in the aromatics. The heavy atom effect of the silver is responsible for this enhancement in phosphorescence. Aromatics such as naphthalene, perylene, anthracene and pyrene were involved in this study. Stern Volmer plots were studied by performing the quenching studies. The quenchers employed were both heavy metals such as silver and thallium and lighter metal like potassium. Dynamic quenching as the predominant phenomenon was noticed.

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Highly correlated quantum chemical methods have been appliedto study the photophysical properties of substituted benzenes.With the inclusion of spin-orbit coupling, the phosphorescencesof these molecules have been calculated usingMulti-CongurationalSelf- Consistent Field (MCSCF) quadraticresponse theory. The Herzberg-Teller approximation has beenadopted to evaluate the vibronic contributions tophosphorescence. The performance of hybrid density functional theory (DFT) atthe B3LYP level is examined in comparison to the MP2, CCSD andCCSD(T) methods for the geometry and permanent dipole moment ofp-aminobenzoic acid. The time-dependent DFT/B3LYP method isapplied to calculate the two-photon absorption of a series ofZinc-porphyrin derivatives in combination with a two-statemodel. The transitions between excited singlet and tripletstates of Zinc and Platinum based organometallic compounds havebeen computed using DFT quadratic response theory. The resultsare used to simulate the non-linear propagation of laser pulsesthrough these materials utilizing a dynamical wave propagationmethod.

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