Enhancement of Fluorescence in Colloidal CuInS 2 Nanocrystals by Introduction of Crystal Defect
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1176-Y03-12
Enhancement of Fluorescence in Colloidal CuInS2 Nanocrystals by Introduction of Crystal Defect Masato Uehara1, Kosuke Watanabe 2, Yasuyuki Tajiri 2, Hiroyuki Nakamura 1 and Hideaki Maeda 1,2,3 1 Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 807-1, Shuku, Tosu, Saga, 841-0052, Japan 2 Department of Molecular and Material Sciences, Interdiscplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka, 816-8580, Japan. 3 CREST, Japan Science and Technology Agency, 4-1-8, Hon-chou, Kawaguchi, Saitama, 3320012, Japan ABSTRACT Cu-In-S nanocrystals were developed as a low toxic fluorescent. The stoichiometric CuInS2 nanocrystals were synthesized facilely by heating a solution of metal complexes. The fluorescence would be originated from the crystal defect. We intentionally introduced the crystal defects related to Cu deficiency in nanocrystal with the prospect that the fluorescence intensity would be increased. The nanocrystals have many defects without phase separation as observed in bulk material. Consequently, the fluorescence quantum yield achieved to c.a. 6%. Moreover, the fluorescence quantum yield was increased up to 15% by the ZnS-coating.
INTRODUCTION Semiconductor nanocrystals (NCs) with high colloidal stability and well-defined particle size distribution have been synthesized in organic solvent [1]. They have also received much attention because of their many applications. In particular, CdSe have been anticipated for use in bio-tag [2]. Nevertheless, this material includes toxic elements (Cd and Hg). These elements are regulated by RoHS and WEEE. In this study, Cu-In-S NCs were developed as a low toxic fluorescent. It has been difficult to obtain the high crystallinity NCs in ternary material CuInS2. To our knowledge, the reported fluorescence of CuInS2 NCs originates not from the band exciton recombination but from the donor-acceptor (D-A) transition, which are related to crystal defects, and the quantum yield was low [3, 4]. We intentionally introduced the crystal defect in CuInS2 NCs with the prospect that the fluorescence intensity would be increased. We tried to introduce and control the defect structure of nanocrystals. The stoichiometric CuInS2 nanocrystals were synthesized facilely by heating a solution of metal complexes and dodecanethiol. The fluorescence would be originated from the crystal defect. We introduced the crystal defect in nanocrystal by the alteration of the elemental ratio in the raw material solution. The defect structure of products was analyzed using Raman spectroscopy and other techniques. EXPERIMENT
The synthesis was carried out in the low toxic system. Copper Iodide (I) and indium Iodide (III) were separately dissolved in oleylamine (0.166 mol/L). Elemental sulfur was dissolved into octadecene (0.166 mol/L). These solutions were mixed at the requested ratio and diluted into octadecene with 10% dodecanthiol. This raw material solution was heated at 160240 ºC in a ves
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