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

• Published in: Magnetic resonance in chemistry Vol. 40; no. 6; pp. 381 - 386
• Main Authors: Purnell, Ian J., Chiesa, Mario, Farley, Robert D., Murphy, Damien M., Rowlands, Christopher C., Cristina Paganini, Maria, Giamello, Elio
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01-06-2002
• Subjects: colour centres; ENDOR; ESR; oxides; surface
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.1028

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 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.