Silica optical absorption

The optical absorption spectra of Au-implanted silica samples annealed in air or Ar for 1 h at different... 

Figure 7. Optical absorption spectra of Au-implanted silica samples atmealed in air (a) or Ar (b) for 1 h at different temperatures, (c) Nonlinear fit (empty circles) to the optical absorption spectrum of the sample annealed at 900 °C in air, from which the average cluster diameter is obtained and compared to the TEM measured one, (d) Evolution of the optical spectra of Au-...

The introduction of 2-[4-(dimethylamino)phenylazo]benzoic acid into a silica sol allows the preparation of pH-sensitive doped coatings upon glass substrates. The behavior of this system was evaluated as the function of pH changes in liquid and gas media68. Optical absorption and sensitivity against pH were monitored by Vis spectroscopy. Chemical and mechanical stability tests carried out with coatings demonstrated that they were resistant enough to be use in sensor devices for pH measurements in laboratories. 

Carbon dioxide gas (CO2) exhibits a set of relatively strong absorption bands at approximately 2 pm, which coincides with the infra-red edge of the transmission band of silica optical fibres (see Figure 6). These absorption... 

Optical absorption, of hydrogenated and hydrogen- free films, 17 206 Optical amplifiers, 11 145-146 Optical applications U.S. patents in, 12 614t of vitreous silica, 22 440-441 Optical cavities, 14 849 Optical cells, for high pressure measurements, 13 417-419 Optical coatings, cerium application,... 

Fig. 7.15. Optical absorption spectra (a) of the surface and the bulk silyl radicals in silica (data for bulk centers adapted from Ref. [46]) and correlation diagram (b) between EPR and optical properties for silyl-type radicals in silica.

The SCs at the silica surface readily react with molecular oxygen. This reaction is convenient to monitor optically (Figure 7.23a). Oxygen chemisorption is accompanied by the disappearance of the optical absorption band of SCs. The adsorption of one molecule leads to the decay of one SC. Quantum-chemical calculations show that the three-member cyclic symmetric structure (Figure 7.24) is the most stable product of oxygen addition to the SC [74] ... 

Silicon films that were electron beam evaporated at a rate of 5 nm sec-1 on silica substrates at 440°C were subsequently irradiated with an Ar+ laser. The rapidly scanned Gaussian beam formed a smooth lateral temperature gradient in the film hence it provided a simple means to study the crystallization mechanism. The laser-heated track reveals two easily discernible areas. A 1 -//m-thick film showed color changes from black to deep red at the margins of the track to light yellow in the middle of the track. Despite the smooth fall of the laser intensity, the different boundaries are abrupt. Optical absorption measurements of the respective areas are also displayed in Fig. 1. The curve E440 represents the as grown evaporated film and is in... 

The various probe beams can be coupled into the same singlewavelength, dual-channel pulse-probe transient optical absorption set-up. A one-meter-long optical delay line is used to control the variable time delay between the electron and the probe pulses. Approximately half of the probe beam is deflected onto a reference photodiode while the other half of the beam is slightly focused into the sample, which is placed in front of the output window of the accelerator. Subsequently, the probe beam is then transported to the sample photodiode. (Alternatively, in some laboratories the probe and reference beams are transported into the detection room by long, low-OH silica optical fibers in order to reduce electronic noise pickup on the detector signal cables.)... 

Ultraviolet absorption by sulfur dioxide may also be usefully applied in the field for direct plume observations. In a novel technique developed for the observation of the colorless discharge of sulfur dioxide and water vapor from a natural gas cleaning plant vent stack, the use of silica optics and a special UV sensitive film allowed the clear photographic observation of plume behavior from the ultraviolet absorption of the sulfur dioxide component [30]. 

Color." The most obvious effect produced in silica gel by radiation is a grayish-purple color (64), which can be almost surely attributed to the same type of center as that responsible for the similar color in irradiated quartz, namely, a positive hole trapped at an oxygen ion adjacent to a substitutional Al + impurity ion (65-67). The attribution rests on the similarity in optical absorption between irradiated gel and irradiated quartz (66), on the dependence of the intensity of the color on the aluminum content (69), and on the observation of a hyperfine interaction characteristic of the spin of the 2 a1 nucleus (I = 5/2) in the ESR spectrum of the irradiated gel (70). Furthermore, the ESR sextet and the color are annealed at comparable rates above 200° (70) and are both destroyed by adsorption of H2 at room temperature (64, 70). Their intensities increase in parallel as the aluminum content, the severity of preirradiation heat treatment, or the length of irradiation is increased (70). The concentration of the center does not increase indefinitely. After some lO i ev/gm, it approaches a limiting value which depends on the impurity content, for typical gels around lO H2/gm (69). 

Optical absorption spectra were measured using the glass and composite samples of 2-4 mm thickness in the IR, visible- and UV-regions. The pore-size distribution in the gel structure measured by BET-method has a complex character the network contains micro- (3.0 nm), meso- and macro-pores (5-25 nm). The pore size can be increased by chemical attack of silica network by fluorine ions in solution and also in vapor phase until heating and dissociation of F-containing compounds (HF, NH4F). 

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