We use chemical vapour deposition (CVD) for the synthesis of pure and doped MgO nanoparticles[1]. In this presentation we demonstrate how the admixture of a second metal component alters the electronic surface properties of MgO nanocrystals. When MgO nanoparticles are doped with monovalent Li-ions, traces of a dopant already induce dramatic changes in the optical and chemical surface properties. Isovalent Ca²⁺ cations can be distributed homogeneously in MgO nanocrystals although CaMgO mixtures are thermodynamically forbidden on a macroscopic scale. Subsequent thermal activation leads to calcium ion segregation into the MgO surface. These CaMgO nanocrystals represent novel materials with enhanced surface basicity and a higher thermal stability in comparison to pure MgO[2]. Furthermore, an unexpected photonic behaviour of those mixtures is reflected by dramatically increase in photoluminescence emission which is also red-shifted with respect to pure MgO. On the contrary, the admixture of also isovalent but larger Sr²⁺ cations induces a blue-shifted emission irrespective of the excitation wavelength.
It is known that by mixing MgO (band gap 7,8 eV) with ZnO (band gap 3,4 eV), one can tune the band gap[3]. However, the effect of ZnO on the surface electronic structure of MgO in terms of optical absorption and emission effects is so far unexplored. Therefore, surface studies on powdered Mg_xZn_x-1O samples are currently carried out in our lab in order to elucidate whether such materials represent interesting candidates for light-induced conversion of an insulating metal oxide into a persistent electronic conductor.

[1] S. Stankic et al. Angew. Chem. Int. Ed. 44 (2005) 4917
[2] S. Stankic et al. Nano Letters 5 (2005) 1889
[3]I. Takeuchi et al. J. Appl. Phys. 94 (2003) 7336

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