Photolytic production of Fe3+ in CaS |
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Authors: | Daniel C. Harris Josephine Covino Marian E. Hills Robert W. Schwartz |
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Affiliation: | Chemistry Division, Research Department, Naval Weapons Center, China Lake, CA 93555, U.S.A. |
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Abstract: | Calcium sulfide powder containing iron as an impurity was irradiated with 580, 366 or 254 nm light at 77 K. Irradiation enhanced a broad (16 G peak-to-trough) electron paramagnetic resonance (EPR) signal at g = 2.017 and caused six sharp (~1 G) lines to appear in the X-band EPR spectrum at 347, 529, 956, 1963, 3547 and 5376 G. Enrichment of CaS with Fe2+ produced samples with similar photochemistry. It is proposed that irradiation causes the reaction Fe2+ + trap → Fe3+ + trap?, whose products give rise to six sharp EPR lines assigned to Fe3+ and a broad line associated with trap?. Both hyperfine splitting by 57Fe (13 G) and superhyperfine splitting by 33S (11.4 G) are observed in the six line spectrum. The environment of the photo-generated Fe3+ has less than octahedral symmetry. V2+ was observed at octahedral sites in unirradiated CaS for the first time, and is characterized by the EPR parameters g = 1.961 and A (hyperfine coupling) = 74.6 × 10?4 cm?1. EPR signals due to Mn2+ and Cr3+ at octahedral sites and Fe3+ at a low symmetry site were also observed in unirradiated CaS. |
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