Research Papers in Physics and Astronomy

 

Date of this Version

June 1967

Comments

Published by American Physical Society. Phys. Rev. Lett 18, 1123 (1967). http://prl.aps.org. Copyright © 1967 American Physical Society. Permission to use.

Abstract

This Letter reports an investigation using pulsed electron irradiation to determine if the low efficiency of F-band coloration in calcium fluoride is caused by the instability of the F center. No transient F centers were seen in times as short as 2 x 10-7 sec. It is concluded that the inherent efficiency of F-band coloration in CaF2 is small compared with similar processes in alkali halides and a possible reason for this is discussed.

Calcium fluoride has been extensively studied and is found to be more difficult to color than alkali halides and to have absorption spectra which vary widely with coloration method, crystal origin, and impurity content.

Two intrinsic color centers have been observed in CaF2 by electron spin-resonance techniques. One is the VK or self-trapped hole, whose resonance has been reported by Hayes and Twidell2 in x-rayed CaF2 at liquid-nitrogen temperatures (LNT). The other is the F center, an electron trapped in an anion vacancy, whose resonance has been found by Arends3 in additively colored crystals and correlated with an optical absorption band at 375 nm4.

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