resumo
Transparent monoliths of urea cross-linked tripodal siloxane-based hybrids, named tri-ureasils, were prepared by the solgel process, using a wide concentration range of hydrochloric acid catalyst (1.0 x 10(-3) = [HCl] <= 2.0 M). The gelation time of the monoliths was controlled by varying the amount of water (2.2 and 22.2 mmol) and HCl (between 4.0 x 10(-5) and 8.0 x 10(-2) mmol) incorporated. Their local structure was characterized by X-ray diffraction, Si-29 and C-13 nuclear magnetic resonance, mid-infrared and ultraviolet/visible absorption spectroscopy, and photoluminescence in steady-state and time resolved modes. The effect of [HCl] in the enhancement of the emission quantum yield was quantified. Although all the hybrids display emission at room temperature in the blue spectral region, it was observed that maximum and constant quantum yield values of 0.13 +/- 0.01 are achieved for 0.01 <= [HCl] <= 0.1 M.
palavras-chave
CARBOXYLIC-ACID SOLVOLYSIS; METAL ACTIVATOR IONS; BRIDGED SILSESQUIOXANES; LIGHT EMISSION; PHOTOLUMINESCENCE; PHOSPHORS
categoria
Chemistry
autores
Freitas, VT; Lima, PP; Bermudez, VD; Ferreira, RAS; Carlos, LD
nossos autores
Luís Carlos
Professor Catedrático
Maria Rute de Amorim e Sá Ferreira André
Professor Catedrático
Patrícia Pereira Lima
Bolseiro de pós-Doutoramento
Vânia Patrícia Castro Teixeira Freitas
Bolseiro de investigaçãoProjectos
agradecimentos
This work was financed by Fundo Europeu de Desenvolvimento Regional (FEDER), COMPETE, and Fundacao para a Ciencia e a Tecnologia (FCT) (contracts PEst-C/CTM/LA0011/2011, PTDC/CTM-BPC/112774/2009, SFRH/BPD/34365/2006) and the Portuguese National NMR Network (RNRMN).