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Monodisperse Mesoporous Silica Microspheres Formed by Evaporation-Induced Self Assembly of Surfactant Templates in Aerosols

✍ Scribed by G.V. Rama Rao; G.P. López; J. Bravo; H. Pham; A.K. Datye; H.F. Xu; T.L. Ward


Publisher
John Wiley and Sons
Year
2002
Tongue
English
Weight
174 KB
Volume
14
Category
Article
ISSN
0935-9648

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✦ Synopsis


The oligomer synthesis and the physical characterizations have been published elsewhere [15]. The thin solid films of pure oligomers were prepared by spin-coating from the chloroform solution at 0.8 and 0.1 % w/w respectively or by evaporation under 10 ±6 mbar vacuum. The films in PVK for DFB measurements were obtained by dissolution of the oligomers at concentrations ranging between 5 and 50 %. The films were spin-coated onto glass substrates. Absorption and photoluminsecence were recorded respectively with a Hitachi U-3000 spectrometer and PTI LPS-220B spectrofluorimeter. Light intensities were measured with a 1 cm 2 area Hamamatsu silicon photodiode. U PL was measured in solid films using an integrating sphere (TRC-060-SL from Labsphere) and a laser excitation at 411 nm (PPm04 from Power Technology). The integrating sphere is a hollow sphere, coated inside with a diffusely reflecting material. The flux received at an aperture in the sphere (the exit port) is proportional to the total amount of light within the sphere, irrespective of its angular distribution. The samples were measured under pure nitrogen atmosphere and U PL was calculated by taking into account the incident light absorbed directly by the polymer film and after internal reflection [26].

The experimental DFB setup was presented elsewhere [23]. The pump source was a frequency tripled Q-switched mode locked Nd:YAG delivering 33 ps pulses at a 10 Hz repetition. The spot size of the beam on the film was 210 ±3 cm. The emitted beam was collected from the glass slide waveguide into an optical fiber coupled with a spectrometer.