title: Revealing the Cu(2+) ions localization at low symmetry Bi sites in photorefractive Bi12GeO20 crystals doped with Cu and V by high frequency EPR.
abstract: The sites of incorporation of Cu(2+) impurity ions in Bi12GeO20 single crystals co-doped with copper and vanadium have been investigated by electron paramagnetic resonance (EPR). While the X-band EPR spectra consist of a simple broad (ΔB ∼50 mT) line with anisotropic lineshape, the W-band EPR spectra exhibit well resolved, strongly anisotropic lines, due to transitions within the 3d(9)-(2)D ground manifold of the Cu(2+) ions. The most intense group of lines, attributed to the dominant Cu(2+)(I) center, displays a characteristic four components hyperfine structure for magnetic field orientations close to a 〈110〉 direction. The g and A tensor main axes are very close to one of the 12 possible sets of orthogonal 〈1-10〉, 〈00-1〉 and 〈110〉 crystal directions. Several less intense lines, with unresolved hyperfine structure and similar symmetry properties, mostly overlapped by the Cu(2+)(I) spectrum, were attributed to Cu(2+)(II) centers. The two paramagnetic centers are identified as substitutional Cu(2+) ions at Bi(3+) sites with low C1 symmetry, very likely resulting from different configurations of neighboring charge compensating defects.
authors: National Institute of Materials Physics, POB MG 7, 077125 Magurele, Romania. Electronic address: snistor@infim.ro.
authors: Sergiu V
authors: SV
authors: Nistor
authors: National Institute of Materials Physics, POB MG 7, 077125 Magurele, Romania.
authors: Mariana
authors: M
authors: Stefan
authors: Physics Department - CDE, University of Antwerp, Universiteitsplein 1, 2610 Antwerpen (Wilrijk), Belgium.
authors: Etienne
authors: E
authors: Goovaerts
authors: Institut Langevin, Ondes et Images, ESPCI ParisTech, PSL Research University, CNRS UMR 7587, INSERM U979, Université Paris VI - Pierre et Marie Curie, 1 rue Jussieu, 75005 Paris, France.
authors: François
authors: F
authors: Ramaz
authors: Institut Langevin, Ondes et Images, ESPCI ParisTech, PSL Research University, CNRS UMR 7587, INSERM U979, Université Paris VI - Pierre et Marie Curie, 1 rue Jussieu, 75005 Paris, France. Electronic address: briat.bernard@wanadoo.fr.
authors: Bernard
authors: B
authors: Briat
keywords: Bi(12)GeO(20); Cu(2+); High frequency EPR