Corantes com transferência protônica em meios poliméricos como meio ativo para sistemas de laser

• Autor(a) principal: Taüber, Utz Wolgang
• Data de Publicação: 2006
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal Fluminense (RIUFF)
• Texto Completo: https://app.uff.br/riuff/handle/1/18919
• topic: Laser; Corantes; Polímeros; Espectroscopia; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

In the present work we studied the characteristics of the dyes 2-(2 - hydroxyphenyl)benzimidazole (HPBI) and 2-(2 -hydroxy-5 -chloro)benimidazole (Cl-HPBI) dissolved in solid polymeric hosts. These dye molecules show an excited state intramolecular proton transfer (ESIPT). The polymers used as host materials are polymethylmetacrylate (PMMA), polystyrene (PS) and the alternating copolymer PS-co- PMMA. Apart from their role in spectroscopic investigations, the samples were also used as active material to produce Amplified Spontaneous Emission (ASE). The emission and photodepletion characteristics of the dyes in the host material were observed. The samples of the PS-co-PMMA copolymer, a polymer that has never been used before as host material, show major efficiency and minimal photodepletion. On the other hand, the dyes in PMMA, a polymer that is widely used as a solvent for dyes, show major photodepletion. A comparison of the photophysical parameters of the samples with the experimental results indicate that the emission cross section has a great influence on emission efficiency and photodepletion. A kinetic model was developed in this work to analyze the experimental observations. Due to the experimental conditions that allow only first order processes, the model consists of six energy levels of the molecules, these being the following: the first excited singlet and triplet levels as well as the ground levels of normal and tautomer forms of the molecule. The model accurately reproduces the temporal profiles of the ASE. Experimentally observed photodepletion, introduced in the model as photodegradation starting from the upper emission level, is reproduced very well for most of the samples. The results of the calculations show that the ratio between the cross section of emission and reabsorption of emission wavelength is crucial for both efficiency and photodepletion.