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  Enhanced Luminescence and Photomagnetic Properties of Surface-Modified EuO Nanocrystals

 

Europium(II) oxide (EuO) has localized narrow 4f orbitals that exist as the degeneracy levels between the conduction band (5d orbitals of EuII) and the valence band (2p orbitals of O2-). The 4f-5d electron transition and spin configuration of EuO lead to unique optical, magnetic and electronic properties. In fact, the theoretical quantum-confinement model predicts the enhanced luminescence and specific magnetic properties of nano-sized Eu(II) semiconductor. Whereas bulk EuO has been prepared by thermal reduction of Eu2O3 at more than 1000 °C, EuO nanocrystals have never been synthesized and isolated until recently. In this paper, we report the smaller EuO nanocrystals (average diameter: 3.4 nm) synthesized by the photochemical reduction of Eu(NO3)3 in methanol. The EuO nanocrystals exhibited two unconventional photophysical properties; emission quantum yield of the EuO nanocrystals in methanol was 49±5% at 300K, which is the highest efficiency reported for EuO, and their magnetization increases dramatically under UV irradiation at room temperature. The mechanism of the photo-magnetization increase should be attributable to the presence of an exciton band in the UV region in accordance with the highly efficient luminescence from the polyurea modified EuO nanocrystals. The polymers containing EuO nanocrystals are expected to be highly useful in future devices, such as plastic photo-isolators for optical fiber and future photomagnetic devices.  

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