Bulk and Surface Excitons in Alloyed and Phase-Separated ZnO鈥揗gO Particulate Systems

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• 作者：Huanjun Zhang ; Amir R. Gheisi ; Andreas Sternig ; Knut M眉ller ; Marco Schowalter ; Andreas Rosenauer ; Oliver Diwald ; Lutz M盲dler
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2012
• 出版时间：May 23, 2012
• 年：2012
• 卷：4
• 期：5
• 页码：2490-2497
• 全文大小：490K
• 年卷期：v.4,no.5(May 23, 2012)
• ISSN：1944-8252

文摘

The rational design of composite nanoparticles with desired optical and electronic properties requires the detailed analysis of surface and bulk contributions to the respective overall function. We use flame spray pyrolysis (FSP) to generate nanoparticles of the ternary Zn鈥揗g鈥揙 system the compositions of which range from solid solutions of Zn²⁺ ions in periclase MgO to phase separated particle mixtures which consist of periclase (cubic) MgO and wurtzite (hexagonal) ZnO phases. The structure and composition of the composite Zn_xMg_1鈥?i>xO (0 鈮?x 鈮?0.3) particles are investigated using X-ray diffraction and high-resolution transmission electron microscopy, whereas UV diffuse reflectance and photoluminescence (PL) spectroscopy are used for the investigation of their optical properties. Vacuum annealing has been carried out to track the effects of stepwise elimination of surface adsorbates on the photoexcitation and PL emission properties. We demonstrate that for Zn_0.1Mg_0.9O particles, the admixed ZnO suppresses the MgO specific surface excitons and produces a PL emission band at 470 nm. Although gaseous oxygen partially reduces the emission intensity of hydroxylated particles, it leads to entire quenching in completely dehydroxylated samples after vacuum annealing at 1173 K. Consequently, surface hydroxyls at the solid鈥揼as interface play a significant role as protecting groups against the PL-quenching effects of O₂. The obtained results are relevant for the characterization of ZnO-based devices as well as for other metal oxide materials where the impact of the surface composition on the photoelectronic properties is usually neglected.

Keywords:

composite; aerosol; nanoparticle; doping; photoluminescence; photoelectronic