F-Centres of Two Types in BaFCl Crystals

✍ Scribed by E. Nicklaus; F. Fischer

• Publisher: John Wiley and Sons
• Year: 1972
• Tongue: English
• Weight: 484 KB
• Volume: 52
• Category: Article
• ISSN: 0370-1972
• DOI: 10.1002/pssb.2220520214

✦ Synopsis

Abstract

F‐centres in X‐irradiated and additively coloured tetragonal BaFCl single crystals have been studied. An F‐centre at a fluorine site absorbs light polarized parallel to the crystallographic c‐axis in a band at 438 nm and light polarized perpendicular to c in a band at 550 nm. A chlorine F‐centre has a band at 532 nm (E ‖ c) and a double band at 440 nm (E ‖ c). This dichroism arises from the tetragonal surroundings of the F‐centres. The splitting of the double bands is probably due to a dynamic Jahn‐Teller effect. In an X‐irradiated crystal there is a partial transformation of fluorine into chlorine F‐centres. In additively coloured BaFCl predominantly fluorine type F‐centres are formed above 300 °C in thermal equilibrium.