Preparation of Ultraviolet Light Emitting ZnO Nanoparticles Via a Novel Synthesis Route
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Preparation of Ultraviolet Light Emitting ZnO Nanoparticles Via a Novel Synthesis Route Yuntao Li1, Richard D. Yang2, S.Tripathy3, H.-J. Sue1, N. Miyatake4, and R. Nishimura5 Polymer Technology Center, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123 2 Department of Chemistry, Texas A&M University, College Station, Texas 77843 3 Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602 4 KANEKA Texas Corporation, Pasadena, TX 77057 5 KANEKA Corporation, Hyogo, Japan 676-8688 1
ABSTRACT A new synthesis methodology is utilized to prepare ZnO nanoparticles with a narrow size distribution between 2 to 4 nm. The particle growth is found to be reaction time dependent. The dry powders of ZnO nanoparticles show a strong blue-shifted near-band-edge ultraviolet emission, and the size and size distribution of the particles did not exhibit noticeable change during solvent evaporation. Raman spectra show ZnO E22 (TO) phonon mode and other vibration modes that are attributed to the bound acetate group. The CO stretching mode in the Raman spectra is red-shifted to 1401 cm-1, indicating a strong adsorption of the acetate ligands onto ZnO surfaces. INTRODUCTION ZnO-based materials have attracted enormous attention in recent years because of their remarkable properties for electrical and optoelectronics applications [1]. As a large bandgap material (3.3 eV at room temperature), the most promising application for ZnO is demonstrated on ultraviolet (UV) emitting devices. Semiconductor materials, including ZnO, show both improved quantum yield and tunable excitonic emission energy at nanometer size region. Desirable UV emission from ZnO materials can be obtained by preparing nano-sized particles and controlling their surface chemical properties. A number of synthesis methods have been reported to successfully prepare ZnO nanocrystals in the forms of solid thin films [2] or colloidal solutions [3]. Among these methods, the hydrolysis of zinc acetate salts in alcohol has been extensively investigated to obtain monodispersed ZnO nanoparticles [3]. However, it has been observed that the UV emission band is strongly quenched in those experiments [2,3]. Instead, the predominant green emission peak is seen, which is attributed to the deep trap level from oxygen vacancies on the surface [4]. Poly(vinyl pyrrolidone) (PVP) has been used to cap ZnO nanoparticle surfaces to enhance the UV luminescence [5]. Other capping molecules, such as tetraoctylammoniumbromide (TOAB), have also been used in electrochemical growth of ZnO nanoparticles to quench the green emission of the nanoparticles [6]. However, both methods are limited for device applications due to the low yield nature of the nanoparticles (precursor concentration
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