Sistemas h?bridos luminescentes, tipo absorvedor-emissor de energia, para aplica??o em sensores de radia??o.

Programa de P?s-Gradua??o em Engenharia de Materiais. Departamento de Engenharia Metal?rgica, Escola de Minas, Universidade Federal de Ouro Preto.V?rios processos m?dicos e industriais utilizam radia??o como tratamentos de materiais e pacientes. Neste contexto, o objetivo deste trabalho ? o desenvolvimento de sistemas luminescentes vers?teis, tipo absorvedor-emissor de energia, para aplica??o como sensores de radia??o em uma ampla faixa espectral: raios-X (Tubo de Cobre ? 40 Kv, 40 mA), radia??o Gama (1,33 Mev), luz azul (??= 450 nm) e UV (??? 300 nm). As principais caracter?sticas desses sistemas s?o: (1) a fotodegrada??o do poli(2-met?xi,5-etil(2-hexil?xi)p-fenilenovinileno) (MEH-PPV), atrelado a altera??o de cor e da sobreposi??o dos espectros de absor??o desse pol?mero com a emiss?o induzida pela radia??o de Tungstato de C?dmio (CdWO4), e (2) a emiss?o de pontos qu?nticos ? Quantum Dots (QDs) de Seleneto de C?dmio Zinco (CdZnSe) e Seleneto de C?dmio Enxofre (CdZnS) com tamanhos diferentes. Filmes, em matriz de poliestireno (PS), e solu??es desses materiais foram preparados e, em seguida, as propriedades ?ticas dos sistemas foram investigadas por meio das t?cnicas de espectrofotometria de absor??o no UV-Vis (ABS), fotoluminesc?ncia (PL) e diagrama de cromaticidade. Como resultado, observa-se a depend?ncia direta da resposta dose-cor a composi??o qu?mica dos sistemas. Como principal resultado, observa-se que ? poss?vel adequar a combina??es de materiais luminescentes para aplica??o a determinada faixa de energia de radia??o. Para filmes expostos a luz UV, por exemplo, observa-se resposta mais r?pida com o aumento da massa de CdWO4. J? os QDs, apresentam efici?ncia qu?ntica de at? 80% expostos a UV, e varia??o da fotoemiss?o de 430 a 670 nm. Para filmes expostos de PS/MEH-PPV a luz azul, observa-se queda de 90% na intensidade de emiss?o com doses terap?uticas. Por outro lado, a resposta desse filme com CdWO4 a radia??o ionizante, raios-X e gama, observa-se varia??o na resposta ?tica com a massa de CdWO4. A partir desses resultados pode-se concluir que ? poss?vel ajustar o tempo de mudan?a da predomin?ncia da emiss?o dos materiais, e assim da cor de emiss?o do sistema, por meio da simples altera??o da rela??o entre a massa dos materiais. O resultado se torna importante para o desenvolvimento de novos sensores de radia??o, cuja resposta seja indicativa n?o apenas de dose de radia??o, mas tamb?m t?pica de um dispositivo tipo indicador ?Sim? ou ?N?o?, quando necess?rio. Neste caso, ?Sim? indicaria que a dose de radia??o requerida foi atingida, e ?N?o? que a dose de radia??o foi inferior a necess?ria.Several medical and industrial processes employ radiation materials and patient treatments. In this context, the main goal of this work is to develop versatile luminescent systems, energy absorber-emitter type, for use as radiation sensors in a wide spectral range: X-ray (Copper Tube - 40 kV, 40 mA), radiation gamma (1.33 MeV), light blue (?????450 nm) and UV (????300 nm). The main features of these systems are: (1) the photodegradation of poly (2-methoxy,5-ethyl(2-hexyloxy)p-phenylenevinylene) (MEH-PPV), associated to color change and the overlap of the absorption spectra of the polymer with the emission induced by radiation of Cadmium tungstate (CdWO4) and (2) the emission of selenide Cadmium Zinc (CdZnSe) and selenide of cadmium sulfur (CdZnS) Quantum Dots (QD) with different sizes. Films, in polystyrene (PS) matrix, and solutions of these materials were prepared and then the optical properties of the systems were investigated by measurements of absorption spectrophotometry in the UV-Vis (ABS), photoluminescence (PL) and chromaticity diagram. As a result, there is a direct dependency on the dose-color response with the chemical composition of the system. As the main result, we observe that it is possible to adjust the combinations of luminescent materials for application to a particular radiation energy range. For films exposed to UV light, for example, it is observed faster response with increased mass CdWO4. Since the QDs, exhibit quantum efficiency up to 80% exposed to UV and photoemission variation of 430 to 670 nm. For PS/MEH-PPV film exposed to blue light, there was decrease of 90% in emission intensity at therapeutic doses. On the other hand, the response of the CdWO4 film with ionizing radiation, X-ray and gamma, it is observed variation in optical response with the mass of CdWO4. From these results it can be concluded that it is possible to adjust the time of change on prevalence of the emission of materials, and thus the emission color of the system, by simply changing the ratio of the mass of material. The result becomes important for the development of new radiation sensors whose response is indicative not only of radiation dose, but also typical for a device type indicator "Yes" or "No" when necessary. In this case, "Yes" would indicate that the required radiation dose was reached, and "No" that the radiation dose was less than required