Minerals charge transfer electronic transition

The electronic spectra of a variety of transition metal-bearing oxide and silicate minerals have been measured at high pressures and/or elevated temperatures. Trends for absorption bands originating from crystal field (CF), metal-metal intervalence charge transfer (IVCT) and oxygen —> metal charge transfer (OMCT) transitions are summarized in tables 9.2,9.3 and 9.4, respectively. 

Optical Spectra. The optical properties of smectites have been studied by various workers (32,37-40), and involve several different types of electronic transitions. One important type of transition is the intervalence charge transfer (IT), which is observed in the optical spectra of minerals containing both Fe2 and Fe3 in their... 

Vivianite, Fe2+3(P04)2.8H20, is the classic example of a mineral showing an intervalence charge transfer transition (Wherry, 1918 Bums, 1981). Vivianite has a diagnostic indigo-blue colour and a well characterized Fe2+ —> Fe3+ IVCT absorption band in the polarized spectra illustrated in fig. 4.12 and is the datum with which electron interaction parameters for other minerals are compared. The chemical formula of vivianite is not indicative of a mixed-valence compound. However, the pale-green colour of newly cleaved vivianite crystals or fleshly... 

In the previous chapter it was shown how measurements of polarized absorption spectra in the visible to near-infrared region can provide information on such crystal chemical problems as oxidation states of transition metal ions, coordination site symmetries and distortions, cation ordering and the origins of colour and pleochroism of minerals. Much attention was focused in chapter 4 on energies of intervalence charge transfer transitions appearing in electronic absorption spectra of mixed-valence minerals. 

Platonov A, Tarashchan A, Langer K et al (1998) Electronic absorption and luminescence spectroscopic studies of kyanite single crystals differentiation between excitation of FeTi charge transfer and Cr dd transitions. Phys Chem Miner 25 203-212 Porto S, Giordmaine J, Damen T (1956) Depolarization of Raman scattering in calcite. Phys Rev 147 607-614... 

Food Hpids usually contain only trace amounts of minerals. Non-polar triglycerols and waxes have virtually no possibUity of bindig mineral components. The exception is the opportunity for 7T-interaction of unsaturated fatty acids and unsaturated hpids that are able to complex with transition metals, such as silver. The complexes are of the charge-transfer type where the unsaturated compound acts as an electron donor and the Ag+ cation as an electron acceptor. Free fatty adds yield salts with metals. 

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