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F‐Centres of Two Types in BaFCl Crystals
Author(s) -
Nicklaus E.,
Fischer F.
Publication year - 1972
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220520214
Subject(s) - tetragonal crystal system , fluorine , crystallography , materials science , crystal (programming language) , irradiation , perpendicular , dichroism , crystal structure , chemistry , optics , physics , geometry , mathematics , computer science , nuclear physics , programming language , metallurgy
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.