EPR study of chromium centres formed in hexagonal RbMgF3 and RbZnF3 single crystals

EPR measurements have been made on single crystals of RbMgF(3) doped only with chromium or codoped with chromium and lithium. Three kinds of trigonally symmetric Cr(3+) spectra were observed. Strong spectrum observed from codoped RbMF(3) is ascribed to Cr(3+) Li pair centre. Other two centres are identified by considering the signs of the fine structure parameters b(2)(0). Weak spectrum observed from RbMgF(3) doped only with chromium is ascribed to a simply substituting Cr(3+) ion at the Mg(II) in the face-sharing Mg(2)F(9) unit. The spectrum observed after X-ray irradiation for the above crystal is ascribed to a simply-substituting Cr(3+) ion at the Mg(I) site in the single octahedron unit. Similar Cr(3+) centres are identified for hexagonal-RbZnF(3) codoped with chromium and lithium. An empirical rule for the sign and magnitude of the b(2)(0) parameter among the Cr(3+) centres in the hexagonal-BaTiO(3) type fluorides is presented. Site preference substitution by trivalent chromium ion in RbMgF(3) as found. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim