Trivalent glasses

Let us now consider MMCT for the case in which the donating ion is a lanthanide ion with a partly filled 4/ shell M(/")M(d°)CT. The trivalent lanthanide ions with a low fourth ionization potential are Ce, Pr ", Tb ". Their optical absorption spectra show usually allowed 4f-5d transitions in the ultraviolet part of the spectrum [6, 35]. These are considered as MC transitions, although they will undoubtedly have a certain CT character due to the higher admixture of ligand orbitals into the d orbitals. In combination with M(d°) ions these M(/") ions show MMCT transitions. An early example has been given by Paul [36] for Ce(III)-Ti(IV) MMCT in borosilicate glasses. The absorption maximum was at about 30000 cm ... 

The selectivity of glass for alkah metal ions is connected with the presence of oxides of trivalent metals in the glass structure. Zachariasen [450] states that silicate glass has a random cross-linking, where each silicon atom lies in the centre of a tetrahedron formed of oxygen atoms (see planar scheme (6.5.5)). 

Fluoroalkyl copper compounds, 17 143, 144 a-Fluoroalkylidinehydrazines, 33 167 2-Fluoroalky 1 -2 phospha-1,3-dialky 1 -1,3-diaze-tidinones, synthesis of, 14 87 Fluoroanions, trivalent, uranium, 34 94—95 Fluoroantimony compounds, 7 17 Huoroaryl copper compounds, 17 143, 144 Fluoroberyllates anhydrous, 14 267-276 aqueous chemistry of, 14 274-278 glasses, 14 265-267 preparation and properties of, 14 265-267... 

The IV-VI films are usually p-type, both as deposited and after annealing in air. One study, where PbS was deposited from a bath containing hydrazine, found the deposit on glass to be n-type temporarily but converted to p-type on air exposure. By depositing the PbS on a trivalent metal coating (such as Al), the n-type conductivity could be stabilized for a longer time. 

This review will be concerned with fluorescent-lifetime studies upon condensed systems (that is, glasses, liquids, or crystals) containing rare-earth ions, and will to a large extent deal only with trivalent ions pumped by optical means. Laser phenomena themselves will not be considered, because a number of very excellent review articles (5-7) and books (8, 9) already exist on this subject. 

Glasses and Liquids. Gallagher and co-workers (152) examined in some detail the absorption, fluorescence spectra, and fluorescent lifetimes of trivalent europium in a variety of borate glasses. All data were taken at room temperature, and attempts were made to correlate the emission characteristics with various europium-glass interactions. The fluorescentlifetime measurements were made using a stroboscopic technique. 

Pomeroy, M J., Nestor, E., Ramesh, R., Hampshires (2005), Properties and crystallisation of rare earth SiAlON glasses containing mixed trivalent modifiers J. Amer. Ceram. Soc., 88(4), 875-881. 

Measurements of absorption spectra of oxides, glasses and hydrates of transition metal ions have enabled crystal field stabilization energies (CFSE s) in tetrahedral and octahedral coordinations to be estimated in oxide structures (see table 2.5). The difference between the octahedral and tetrahedral CFSE is called the octahedral site preference energy (OSPE), and values are summarized in table 6.3. The OSPE s may be regarded as a measure of the affinity of a transition metal ion for an octahedral coordination site in an oxide structure such as spinel. Trivalent cations with high OSPE s are predicted to occupy octahedral sites in spinels and to form normal spinels. Thus, Cr3, Mn3, V3+... 

Crystal field spectral measurements of transition metal ions doped in a variety of silicate glass compositions (e.g., Fox et al., 1982 Nelson et al., 1983 Nelson and White, 1986 Calas and Petiau, 1983 Keppler, 1992) have produced estimates of the crystal field splitting and stabilization energy parameters for several of the transition metal ions, examples of which are summarized in table 8.1. Comparisons with CFSE data for each transition metal ion in octahedral sites in periclase, MgO (divalent cations) and corundum, A1203 (trivalent cations) and hydrated complexes show that CFSE differences between crystal and glass (e.g., basaltic melt) structures,... 

The neodymium laser is popular because it is a solid state laser. Trivalent neodymium ions are incorporated in a host crystal or glass, at about one atomic percent doping. In the solid state, high concentrations of ions are available as opposed to the gaseous state. Further the host crystal provides mechanical strength and chemical inertness. 

Infrared transmission spectra are shown in Fig. 1 for typical tetravalent-, trivalent-, and divalent-based fluoride glasses. With a refractive index of 1.5 at sodium D-line, fluoride glasses show a nearly constant transmission of 92% throughout the visible and near infrared. The loss is due primarily to 4% reflection at each end-face of the glass sample. 

Fig. 1. Infrared transmission spectra of fluoride glasses. M = trivalent metal ions.

The idea that ions can diffuse as rapidly in a solid as in an aqueous solution or in a molten salt may seem astonishing. However, since the 1960s, a variety of solids that include crystalline compounds, glasses, polymers, and composite materials with exceptionally high ionic conductivities have been discovered. Materials that conduct anions (e.g. and 0 ) and cations including monovalent (e.g. H+, Fi+, Na+, Cu+, Ag+), divalent, and even trivalent and tetravalent ions have been synthesized. A variety of names that have been used for these materials include solid electrolytes, superionic conductors, and fast-ionic conductors. Solid electrolytes arguably provides the least misleading and broadest description for this class of materials. 

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