Rare doping

As shown in Fig. 25.14, the lackof direct correspondence between any Mossbauer component and the ferromagnetic component of the bulk ferromagnetism suggests that the latter in these garnets may arise not only from the rare doped magnetic iron ions but also from the crystal defects. While the MD/CF treatment increased the ferromagnetic moment in both samples, the magnetic sextets did not increase in the Mossbauer spectra in the case of x = 0.02, the sextets even shrink to their half. 

Aziz R A 1984 Interatomic potentials for rare-gases pure and mixed interactions Inert Gases Potentials, Dynamics and Energy Transfer in Doped Crystals ed M L Klein (Berlin Springer) oh 2, pp 5-86... 

There are many ways of increasing tlie equilibrium carrier population of a semiconductor. Most often tliis is done by generating electron-hole pairs as, for instance, in tlie process of absorjition of a photon witli h E. Under reasonable levels of illumination and doping, tlie generation of electron-hole pairs affects primarily the minority carrier density. However, tlie excess population of minority carriers is not stable it gradually disappears tlirough a variety of recombination processes in which an electron in tlie CB fills a hole in a VB. The excess energy E is released as a photon or phonons. The foniier case corresponds to a radiative recombination process, tlie latter to a non-radiative one. The radiative processes only rarely involve direct recombination across tlie gap. Usually, tliis type of process is assisted by shallow defects (impurities). Non-radiative recombination involves a defect-related deep level at which a carrier is trapped first, and a second transition is needed to complete tlie process. 

Dubost H 1984 Speotrosoopy of vibrationai and rotationai ieveis of diatomio moieouies in rare-gas orystais Inert Gases. Potentials, Dynamics, and Energy Transfer in Doped Crystals (Springer Ser. Chem. Phys. 34) ed M L Kiein (Beriin Springer) pp 145-256... 

M. J. F. Digoimet, Rare Earth Doped Fiber Easers andAmp/ifiers, Marcel Dekker, Inc., New York, 1993. 

PO7 and their rare-earth-doped compounds as starting materials for scintillation studies, with the intention of obtaining new scintillation materials with large, light yield and short decay time. 

Superconductivity has also been discovered in rather exotic materials, including the following Buckminsterfullerene (Cgo) doped with ICI Carbon nanotubes (superconductivity in just one direction) Nickel borocarbides, which contain Ni2 B2 layers alternating with R C sheets, where R is a rare earth element such as Er and organic superconductors that contain planar organic cations and oxoanions. Chemists and physicists continue to study these and other families of superconductors. 

Although the role of rare earth ions on the surface of TiC>2 or close to them is important from the point of electron exchange, still more important is the number of f-electrons present in the valence shell of a particular rare earth. As in case of transition metal doped semiconductor catalysts, which produce n-type WO3 semiconductor [133] or p-type NiO semiconductor [134] catalysts and affect the overall kinetics of the reaction, the rare earth ions with just less than half filled (f5 6) shell produce p-type semiconductor catalysts and with slightly more than half filled electronic configuration (f8 10) would act as n-type of semiconductor catalyst. Since the half filled (f7) state is most stable, ions with f5 6 electrons would accept electrons from the surface of TiC>2 and get reduced and rare earth ions with f8-9 electrons would tend to lose electrons to go to stabler electronic configuration of f7. The tendency of rare earths with f1 3 electrons would be to lose electrons and thus behave as n-type of semiconductor catalyst to attain completely vacant f°- shell state [135]. The valence electrons of rare earths are rather embedded deep into their inner shells (n-2), hence not available easily for chemical reactions, but the cavitational energy of ultrasound activates them to participate in the chemical reactions, therefore some of the unknown oxidation states (as Dy+4) may also be seen [136,137]. 

Xu A-W, Gao Y, Liu H-Q (2002) The preparation, characterization, and their photocataly-ticactivities of rare-earth-doped Ti02 nanoparticles. J Catal 207 151-157... 

Liang C-H, Li F-B, Liu C-S, Lu J-L, Wang X-G (2008) The enhancement of adsorption and photocatalytic activity of rare earth ions doped Ti02 for the degradation of orange I. Dyes Pigm 76 477 184... 

El-Bahy ZM, Ismail AA, Mohamed RM (2009) Enhancement of titania by doping rare earth for photodegradation of organic dye (Direct Blue). J Hazard Mater 166 138-143... 

Effect of ultrasound on the photocatalytic decomposition of KI using Ti02 doped with rare earths. 

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