Electron‐Spin‐Resonance Study of Co²⁺ and Ni⁺ Centers in AgCl(Cu, Co, Ni)

Abstract

on the occasion of his 80th birthday Single crystals of AgCl doped with Coz+, NiZt, and Cu2+ are studied by means of electron spin resonance. As-grown AgCl crystals contain three different Co2f centers : called Co2+(cub), Co2+-(ortho) and Co2+(tetra) corresponding to centers in which a substitutional Co2+ ion is either unperturbed, or perturbed by a nearest or by a next nearest cation vacancy. Ultra violet illumination a t 50 K produces Nit and Cu2+ centers and converts the Co2+(cub) centers to Cot centers which are stable up to 80 K. The thermal decay of the latter enhances the Nit concentration. Above 160 K the Ni+ centers are thermally unstable and contribute to the decay of the Cu2+ centers. It is concluded that the presence of Co2+ ions supresses the darken ability of AgCl which is enhanced by the Ni2+ impurity.Mit Co2+, Ni2+ und Cu2+ dotierte AgC1-Einkristalle werden mittels Elektronenspinresonanz untersucht. Urspriingliche AgC1-Kristalle enthalten drei verschiedene Co2f-Zentren: Co2+(kub.), Co2f(ortho) und Coz+(tetra), die Zentren entsprechen, in denen ein substitutionelles Co2+-Ion entweder ungestort ist oder durch eine nachste oder iibernachste Kationenleerstelle gestort ist. Ultraviolett-Bestrahlung bei 50 K ruft Ni+-und Cu2+-Zentren hervor und wandelt Co2f(kub.)-Zentren in Cot-Zentren um, die bis zu 80 K stabil sind. Der thermische Zerfall der letzteren erhoht die Ni+-Konzentration. Oberhalb 160 K sind die Ni+-Zentren thermisch instabil und tragen zum Zerfall der Cu2+-Zentren bei. Es wird angenommen, daB die Anwesenheit von CoZ+-Ionen die Verfarbungsfahigkeit von AgCl unterdriickt, die durch die Ni2t-Storstelle vergroSert wird.

Studies of EPR g-factors on Rutile (TiO2) with Co2+ Ion

“…Thus from the cluster approach, the microscopic formulas of g factors for 3d 7 (Co 2+ ) ions in rhombic octahedral clusters are derived by using the following perturbation method [11]: [16]. The normalization factors N and the orbital mixing coefficients can be estimated from a semiempirical LCAO method [10,13,14].…”

“…Among them, the anisotropic g factors g X , g Y , and g Z for Co 2+ -doped rutile were reported by various researchers [4 -5], however few theoretical studies for these EPR parameters have been made. In order to explain satisfactorily these EPR data, reasonable and quantitative calculations for 3d 7 (Co 2+ ) in rhombic octahedral crystals are required. Tinkham [6] gave the first-order and Robbroeck et al [7] developed second-order perturbation formulas of g i (i = X Y Z)…”

“…In order to explain satisfactorily these EPR data, reasonable and quantitative calculations for 3d 7 (Co 2+ ) in rhombic octahedral crystals are required. Tinkham [6] gave the first-order and Robbroeck et al [7] developed second-order perturbation formulas of g i (i = X Y Z)…”

“…for the 3d 7 ion in rhombic octahedra. In these formulas, although the covalency effect is considered, the configuration interaction due to the admixture among the ground and excited orbital states is omitted and the treatments of the contributions from covalency effect and rhombic crystal field are oversimplified.…”

“…For overcoming the weakness of [10], we present now a cluster approach to the calculation of g i for 3d 7 (Co 2+ ) in rhombic octahedra. In these formulas, the contributions of the covalency effect, the configuration interaction and the rhombic field are considered and the parameters related to the three important contributions can be estimated from the optical spectra and the structural data of the crystal under study.…”