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Heterogeneity of surface colour centres on alkaline earth metal oxides as revealed through EPR/ENDOR spectroscopy

Purnell, Ian J., Chiesa, Mario, Farley, Robert D., Murphy, Damien Martin, Rowlands, Christopher C., Paganini, Maria Cristina and Giamello, Elio 2002. Heterogeneity of surface colour centres on alkaline earth metal oxides as revealed through EPR/ENDOR spectroscopy. Magnetic Resonance in Chemistry 40 (6) , pp. 381-386. 10.1002/mrc.1028

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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 [FS +(H)], by electron trapping at these anion vacancies. The paramagnetic properties of these colour centres were studied by EPR and ENDOR spectroscopy. 1H 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 FS + (H) centre. On MgO and CaO two dominant FS + (H) centres were identified (labelled sites I and II) whereas on SrO three FS + (H) species were found (sites I, II and III). The possible surface sites responsible for electron stabilization are discussed, and include a 3Ccornermono-vacancy, a 4Cmono-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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Publisher: Wiley-Blackwell
ISSN: 0749-1581
Last Modified: 04 Jun 2017 05:06

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