Dopant environment

Direct observation of point defects in metals has been possible by field ion microscopy. Impurity point defects may be usefully investigated by electron microscopy in combination with electron diffraction and electron spectroscopy. Direct observation of the dopant environment in fluorites has been attempted by Catlow et al. (1984) by employing EXAFS in conjunction with computer simulation. 

One of the most important concerns in rare earth doped glasses is to define the dop)ant environment. Hypersensitive transitions are observed in the spectra of all rare earth ions having more than one f electrons. Hypersensitive transitions of rare earth ions manifest an anomalous sensitivity of line strength to the character of the dopant environment [28, 29]. 

All materials will, to some degree, be subject to corrosion and oxidation by their environment, and the critical early stages of attack can often be understood through the use of surface analytical techniques. A similar approach is required to gain an understanding of the fundamental and applied aspects of surface catalysis, which is of great importance in the petrochemical industry. The microelectronics industry has also contributed to the development of modern surface analytical techniques, where there is a necessity to analyse dopant concentration profiles while retaining lateral resolution on the device of better than one micron. 

While the sol-gel matrix can usefully preserve the properties of the dopant, the reverse is also true in that changing the sol gel cage environment may... 

Exciplex methodhas also been proposed for droplet temperature measurement. In an oxygen environment, however, the fluorescence from the exciplex is quenched by the oxygen. In addition, fuel droplets may contain aromatic hydrocarbons that can produce fluorescence emissions, masking the fluorescence spectrum of the dopants used for the temperature determination. 

An efficient, low temperature oxidation catalyst was developed based on highly disperse metal catalyst on nanostructured Ti02 support. Addition of dopants inhibits metal sintering and prevents catalyst deactivation. The nanostructured catalyst was formulated to tolerate common poisons found in environments such as halogen- and sulfur-containing compounds. The nanocatalyst is capable of oxidizing carbon monoxide and common VOCs to carbon dioxide and water at near ambient temperatures (25-50 °C). 

The dopants, dye molecules, in general, have little effect on the toxicity of DDSNs because they are isolated from the environment [3, 11, 23, 118]. However, if the dopants are photosensitizers or some other specialized molecules, they can... 

Instead of considering how the incorporation of a dopant ion perturbs the electronic structure of the crystal, we will face the problem of understanding the optical features of a center by considering the energy levels of the dopant free ion (i.e., out of the crystal) and its local environment. In particular, we shall start by considering the energy levels of the dopant free ion and how these levels are affected by the presence of the next nearest neighbors in the lattice (the environment). In such a way, we can practically reduce our system to a one-body problem. 

Figure 5.1 A scheme of an illustxative optical center, ABg. This particular center consists of a dopant optical ion A in an octahedral environment of B ions.

Chapters 5 and 6 deal with the spectra of optically active centers. The term optically active center corresponds to a dopant ion and its environment (or to a color center), which produces absorption and/or emission bands that are different to those of the pure crystalline host. This is the case for a large variety of optical materials, such as phosphors, solid state lasers, and amplifiers. 

Figure 6.1 shows the mass spectmm of an impurity run in the positive APPI mode and shows both at miz 352 and MH miz 353. This is an example where the mechanisms of proton transfer and electron transfer are both taking place. This can be confusing when dealing with complete unknowns and demonstrates why it is unsuitable for routine use in an open access multi-user environment or by inexperienced users. A better understanding of the processes involved and the role of mobile phase and dopant is required before this can be put to routine use. There are a number of papers published on this topic [20, 21]. 

Isomorphous substitution of iron oxides is important for several reasons. In the electronics industry, trace amounts (dopants) of elements such as Nb and Ge are incorporated in hematite to improve its semiconductor properties. Dopants are also added to assist the reduction of iron ores. In nature, iron oxides can act as sinks for potentially toxic M", M and M heavy metals. Investigation of the phenomenon of isomorphous substitution has also helped to establish a better understanding of the geochemical and environmental pathways followed by Al and various trace elements. Empirical relationships (e. g. Fe and V) are often found between the Fe oxide content of a weathered soil profile and the levels of various trace elements. Such relationships may indicate similarities in the geochemical behaviour of the elements and, particularly for Al/Fe, reflect the environment in which the oxides have formed (see chap. 16). 

Photoinduced electron transfer occurs through excitation of the 400-nm absorption bands of the donor chromophores based on the aminonapthalene-dicarboximide derivatives. The tails of the dopants absorption bands extend to at least 500 nm, which allows for the use of an Ar+ laser. Figure 8 illustrates the ground-state absorption spectra of the donor and acceptor for both the intramolecular and intermolecular charge transfer dopants in toluene. The spectra are similar for all of the dopants, with the exception of 2, which has a 50-nm red-shifted absorption band. The inset illustrates the broadened spectra in the liquid crystalline environment. The extinction coefficient at 457 nm varies from approximately 1000 M-1 cm-1 for 4, 2000 M-1 cm-1 for 1, 5000 M-1 cm-1 for 3, and 10,000 M-1 cm-1 for 2. 

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