Study of Colour Centres in BaCl2 and BaBr2

After additive or electrolytic coloration, BaCl2, and BaBr2, single crystals exhibit F‐centres, whose proper symmetry is C3. The hyperfine spectrum in BaCl2 can be accounted for with the assumption that there exist two types, FI and FII, of F‐centres, and that each hyperfine constant referring to a Ba2+ ion (k) is given by an empirical expression ak = gN A/d , where dk is the distance between the ion k and the F‐centre. The two types of F‐centres have the same g‐tensor with principal values, in the case of BaCl2, gXX = 1.966; gYY = 1.976; gZZ = 1.986. The F‐centres can be optically bleached at room temperature, and then regenerated by heating above 100 °C.