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Heterogeneity of surface colour centres on alkaline earth metal oxides as revealed through EPR/ENDOR spectroscopy
Author(s) -
Purnell Ian J.,
Chiesa Mario,
Farley Robert D.,
Murphy Damien M.,
Rowlands Christopher C.,
Cristina Paganini Maria,
Giamello Elio
Publication year - 2002
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1028
Subject(s) - chemistry , electron paramagnetic resonance , vacancy defect , oxide , spectroscopy , crystallite , ion , metal , alkaline earth metal , crystallography , inorganic chemistry , nuclear magnetic resonance , organic chemistry , physics , quantum mechanics
A variety of surface anion vacancies, or point defects, are created by high‐temperature activation of a series of polycrystalline alkaline earth metal oxides (MgO, CaO and SrO). Subsequent UV irradiation of the activated oxide under a hydrogen atmosphere results in the generation of surface colour centres [F S + (H)], by electron trapping at these anion vacancies. The paramagnetic properties of these colour centres were studied by EPR and ENDOR spectroscopy. 1 H ENDOR spectroscopy revealed that a well defined heterogeneity of trapped electron species exists on each oxide surface, as characterized by the different superhyperfine couplings between the trapped electron and the nearby proton of the F S + (H) centre. On MgO and CaO two dominant F S + (H) centres were identified (labelled sites I and II) whereas on SrO three F S + (H) species were found (sites I, II and III). The possible surface sites responsible for electron stabilization are discussed, and include a 3C corner mono‐vacancy, a 4C mono‐vacancy and an anion–cation di‐vacancy. The results indicate that regardless of the oxide used, a common degree of morphological similarities exists on each oxide. Copyright © 2002 John Wiley & Sons, Ltd.