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0957-K10-12

Optical Properties of Porous ZnO Nanorods Grown by Aqueous Solution Method Sang Hyun Lee1, Hyun Jung Lee2, Takenari Goto1, Meoung-Whan Cho3, and Takafumi Yao1,3 1 Tohoku Univ., Center for Interdisciplinary Research, Tohoku University6-3, Aramaki, Aobaku, Sendai, 980-8578, Japan 2 Tohoku Univ., Graduate School of Environmental Studies, Tohoku University, 07 AramakiAoba, Aoba-Ku, Sendai, 980-8579, Japan 3 Tohoku Univ., Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, 980-8577, Japan

ABSTRACT

ZnO nanorods were synthesized by chemical solution method at low temperature. The surface of nanorods was changed to porous by using thermal annealing and chemical etching. Surface morphology and their optical properties were changed according to annealing and etching condition. Photoluminescence from as-grown ZnO nanorods almost showed defect related emission in wide range from 450~900 nm. After annealing at 500oC, the band-edge emission of ZnO was observed and emission at visible range was changed to green with decreasing red-orange. The surface morphology of ZnO nanorods was transformed to porous by chemical etching and it led to increase the intensity of band-edge emission about three times. The internal quantum efficiency for porous ZnO nanorods, which was calculated from ratio PL intensity at 10K and 300K, is about 21%. Also, the random lasing at porous ZnO nanorods was occurred at high optical excitation by a photon with traveling inside or outside of porous ZnO nanorod gets amplified by injection second photon before leaving porous ZnO nanorods. INTRODUCTION Nano-size materials have been intensively researched due to their unique physical and chemical properties. By controlling their shapes and size, it is possible to improve the efficiency and apply new devices. For example, one-dimensional nanostructures with high aspect ratio such as carbon nanotube (CNT) show excellent field emission properties and have been suggested as a field emitter for field emission display (FED)[1,2]. Various emissions in visible ranges were realized by band-gap control of (CdSe)ZnS according to change the size as well as researched for application at bio-technology[3,4]. Especially, combination between many inherent properties of ZnO and unique properties by nano-size has brought to synergy effects in scientific and technological research. ZnO nanostructures show multifunctional properties such as piezoelectricity, conductivity, optical emission, sensitivity to gases and high immobilization with DNA [5-9]. To apply full advantage of ZnO nanostructures, control the shape and positioning of nanostructures on substrates were necessary. Expansion of the surface area has a great advantage for a device application because it improves the device efficiency. It increases, for example, the attaching sites of dye in dyesensitized solar cell or the reaction sites in the chemical and bio sensors [10,11]. Considering all

these characters, porous materials are suitable structures for a wide variety of app