Identifying
characteristics of
charge transfer transitions in minerals
Stephanie
M Mattson, George R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 91125, USA
Abstract
Criteria used to identify Fe2+ - Fe3+ and Fe2+ - Ti4+
intervalence charge transfer absorption bands in electronic spectra are
reviewed and compared to the characteristics of unperturbed Fe2+ crystal field bands and those that are intensified by interaction with Fe3+.
Band energy is the least definitive diagnostic criterion. Changes in
band intensity with temperature are also of limited value. Large widths
are the most reliable characteristics of charge transfer bands. New
optical absorption spectra are presented for euclase, as well as 80 K
spectra of rockbridgeite, babingtonite and lazulite. Comparison of
optical spectra to magnetic susceptibility measurements for
rockbridgeite and babingtonite provides support for recent theories
regarding the effect of magnetic coupling on the variation of charge
transfer intensity with temperature.
Polarized spectrum of lazulite at 296 K showing the Fe2+ - Fe3+ intervalence charge transfer absorption at about 660 nm.
