Absorption Spectra of Cr3+
in Al2O3 Under Shock Compression



Tsuneaki Goto, Thomas J. Ahrens, and George R. Rossman

 Division of Geological and Planetary Sciences
California Institute of Technoogy
Pasadena, CA  91125


Abstract

Unpolarized absorption spectra of single crystals of Cr3+ doped Al2O3 (synthetic ruby) have measured using a new, time-resolving, dispersive, streak photographic system over the range 350 to 700 nm during a series of shock loading experiments. The crystal field absorptions assigned to the transition 4A2g  ->  4T2g were observed to shift in a series of experiments from 555 ± 1 nm at atmospheric pressure to 503 ± 5 nm at 46 GPa. In a single experiment at 32 GPa the 4A2g -> 4T1g transition was observed to shift from 405 ± 1 to 386 ± 5 nm. The present data extrapolate downwards in compression toward the 10 GPa data of Stephens and Drickamer (1961) although both crystal field absorption energies increase considerably less with com­pression than predicted by the simple ionic point charge model. The single datum observed for the Racah parameter B, 588 ± 38 cm-1 at 32 GPa, is consistant with previous results to 10 GPa and the trend of decreasing B, with compression expected from the divergence of the data from the point charge model due to increasing  covalancy.


last updated: 5-Oct-2020