Efficient near-infrared luminescence and energy transfer in Nd-Bi codoped zeolites
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Efficient near-infrared luminescence and energy transfer in Nd-Bi codoped zeolites
Zhenhua Bai1, Minoru Fujii1, Yuki Mori2, Yuji Miwa1, Minoru Mizuhata2, Hong-Tao Sun3, and Shinji Hayashi1 1 Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan 2 Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan 3 International Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba-city, Ibaraki 305-0047, Japan
ABSTRACT We prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. The emission covers the range of 970~1450 nm, corresponding to the electronic transitions of Nd3+ ions and Bi-related active centers (BiRAC), respectively. The introduction of Bi distinctly broadens the excitation band of Nd3+ in the visible region, and the lifetime of Nd3+ reaches as long as 354 μs. In the zeolite matrix, Bi ions exist as BiRAC and Bi oxide agglomerates. The former one act as a sensitizer of Nd3+ ions, and the latter one act as a blockage to avoid the quenching effect of coordinated water, which enable Nd3+ ions to show efficient near-infrared (NIR) emission even the zeolites contain large amount of coordinated water. The excellent optical and structural properties make these NIR emitting nanoparticles promising in application as laser materials and biological probes.
INTRODUCTION In recent years, much attention has been paid to the research of rare-earth ions doped materials for the potential applications in laser, optical telecommunication, and many other applications [1-6]. Among them, Nd3+ is one of the most investigated near-infrared (NIR) emitting rare-earth ions for two reasons. On one hand, Nd doped materials are commonly used as active media for solid state laser applications [2,3]. On the other hand, for in vivo biological imaging, the optical absorption and light scattering of human tissue are minimal in the NIR region [4]. Rare-earth ions, which are luminescent in this region, such as Nd3+ at 1064 nm, are ideal candidates for in vivo biological probes [4,5]. However, excitation efficiency of Nd3+ is very low due to its forbidden intra-4f transition [3]. Moreover, the intrinsically sharp and discontinuous absorption bands of Nd3+ require lasers as excitation source to realize some functional applications. Thus, it is an interesting topic to realize sensitization of Nd3+ by using active centers with broad absorption bands. Recently, it was found that “bismuth-related active
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centres (BiRAC)” can be exploited as sensitizers of rare earth ions such as Er3+ and Yb3+ [6,7]. Therefore, we also expect that there may be effective sensitization of Nd3+ ions by an energy transfer process from BiRAC. Zeolites are microporous crystalline aluminosilicates with nanosized pores. Their framework is composed of SiO4 and AlO4 tetrahedra units by shari
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