Electron Spin Resonance Study of Ni²⁺ Centers in AgCl(Cu, Ni)

Abstract

Single AgCl crystals doped with Cu2+ and Ni2+ were studied by means of electron spin resonance. As grown crystals contain three different Ni2+ centers which reduce to Ni+ defects under illumination at 50 K with blue light. Six Nit defects were found with tetragonal, orthorhombic, and cubic symmetry. At 101 K the orthorhombic centers transform to the tetragonal defects. The latter become thermally unstable at 135 K and induce the decay of the Cu2+ centers.Mit Cu2+ und Ni2+ dotierte AgC1-Einkristalle werden mittels E P R untersucht. Jungfrauliche Kristalle enthalten drei verschiedene Ni2+-Zentren, die unter Bestrahlung mit blauem Licht bei 50 K zu Ni+-Defekten reduziert werden. Sechs Ni+-Defekte mit tetragonaler, orthorhombischer und kubischer Symmetrie werden gefunden. Bei 101 K werden die orthorhombischen Zentren in tetragonale Defekte transformiert. Letztere werden bei 135 K instabil und verursachen den Zerfall der Cuz+-Zentren.

Reinterpretation of temperature-induced dynamical behavior in the EPR spectrum ofRh2+centers in AgCl

“…A similar effect has been observed for the dominant ͓RhCl 6 ͔ 4Ϫ complex in meltgrown NaCl single crystals, 5 which is also charge compensated by a next-nearest-neighbor cation vacancy along the g x axis and for other complexes, e.g., Ni ϩ -vacancy complexes in AgCl ͑with a 3d 9 2 B 1 ground state͒. 6 At temperatures near the ambient, the appearance of another EPR spectrum was reported, exhibiting cubic symmetry with g iso Ϸ(g x ϩg y ϩg z )/3. If the temperature was further raised to about 400 K, only this cubic center was detected.…”

“…4͒ and has previously also been reported for the Ni ϩ complex in AgCl in the absence of cation vacancies. 6 The presence of this second, nonlocally compensated Rh 2ϩ complex in AgCl single crystals now allows a simple and satisfactory explanation of the temperature dependence of the EPR spectrum. As the temperature is raised, the observed EPR spectrum of the complex compensated by one cation vacancy changes from orthorhombic to tetragonal symmetry, whereas that of the nonlocally chargecompensated complex changes from tetragonal to cubic.…”

Electron spin resonance study of aquated hexachloro-rhodate complexes in AgCl microcrystals

“…Representative examples of these studies are the self-trapped hole ͑STH͒ 6-10 in AgCl, the self-trapped exciton ͑STE͒ 11,12 in AgCl, the shallow electron trap ͑SET͒ 13 and transition metal impurities [14][15][16][17][18][19] in AgCl and AgBr. Various types of samples can be studied including: single crystals, powders of microcrystals, and microcrystals in emulsion layers.…”

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

“…For the analysis of the Co2+(cub) spectrum the mixing of the 4T1(4P) term into the ground doublet is included and one obtains the following relations : = -2/315. 15 A ' 63 (4) Table 1 z. Table 1 and the resulting parameters are given in Table 2.…”