Limitations for light-emitting devices, the application of which range from full colour displays to optical communication systems, arise from the lack of materials that efficiently emit photons of required energy. Usually semiconductors where discrete electronic transitions can be reached by spatial confinement of the bulk are discussed as components for such devices. The respective situation is different for nanometer-sized alkaline earth oxides which are prototypical ionic insulators. Surface excitons with molecular-like properties can exclusively be generated at low coordinated surface sites¹ and give rise to photoluminescence emission in the range between 200 and 600 nm.

High thermal stability, a sharp size distribution and a well-defined particle morphology² make MgO nanocubes a well-suited model system for investigating the surface electronic structure of oxide particles. Unlike MgO nanocubes CaO, SrO and BaO nanoparticles agglomerate in the course of vacuum annealing and produce large grains of ill-defined morphology³. In this contribution, we present a new approach for the production of thermally stable CaO, SrO and BaO thin films supported on MgO nanocubes. UV-Diffuse Reflectance and photoluminescence measurements reveal novel optical properties compared to those of the pure oxide components. These properties will be discussed in terms of low coordinated surface elements that act as excitation and emission sites. Furthermore, chemical surface reactivity changes induced by the second metal oxide component are evidenced by the IR spectroscopic characterization of H₂ activation processes.

¹ Garrone et al. Philos. Mag. 1980, 42B, 683

² Stankic et al. Angew. Chem. Int. Ed. 2005, 44, 4917

³ Stankic et al. J. Phys. Chem.B 2006, 110, 13866

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