Multifunctional GdPO 4 :Pr 3+ nanocrystals displaying UV emission, visible emission, and magnetic properties
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Multifunctional GdPO4:Pr3+ nanocrystals displaying UV emission, visible emission, and magnetic properties Junsang Cho* and Chang Hae Kim Thin Film Materials Research Group, Advanced Materials Division, Korea Research Institute of Chemical Technology (KRICT), Yuseong-gu, Daejeon 305-600, Korea. ABSTRACT Multifunctional Pr3+-doped GdPO4 nanocrystals possessing UV, visible emissions and magnetic properties were synthesized via co-precipitation and following annealing. It was revealed that as-prepared GdPO4 nanorods were transformed to nanoparticles after heat treatment at 900 ºC for 2 hours. Ultimately, GdPO4:Pr3+ nanoparticles have strong UV emission under the excitation of 275 nm and visible emission under the excitation of 445 nm, which offers the optical modalities in both UV and visible range. Moreover, Gd3+-containing nanoparticles are efficient T2-weighted (negative) magnetic resonance (MR) contrast agents due to the presence of Gd3+ ions, which can be potentially applied as multimodal, photoluminescence-magnetic resonance imaging contrast agent. INTRODUCTION Multifunctional materials combine more than one imaging modality such as optical imaging, X-ray computed tomography (CT), positron emission tomography (PET), and magnetic resonance (MR) imaging contained in single vehicle [1-3]. In particular, optical imaging provides its high resolution in bio-imaging and MR imaging offers excellent anatomical depth, non-invasive, and real time monitoring. Hence, a lot of attentions had been paid to the development for the multifunctional nanomaterials combining the two representative modalities such as optical and MR imaging, especially for application in biomedical applications [4]. In recent, Gd3+-based inorganic nanomaterials have attracted much interest because they are able to be used as potential multifunctional nanoplatform. It was well known that a paramagnetic nature of Gd3+ ion arising from seven unpaired electrons in 4f electron shell could be utilized as contrast agents for T1-enhanced MR imaging owing to their enhancement of relaxation of the neighboring protons. In addition, by doping light-emitting various lanthanide ions (Ln3+) into a Gd3+-containing host matrix, novel materials possessing both advantages of fluorescent and magnetic properties could be achievable for multimodal imaging [5-6]. For the research of optical imaging on the multifunctional GdPO4 nanoparticles, the research has been extensively studied only in visible range for up-conversion (UC) emission doped with Yb/Tb and down-conversion (DC) emission doped with Eu or Ce/Tb [7-8]. However, to our best knowledge, there have been no reports on multifunctional GdPO4:Pr3+ nanoparticles having UV and visible emission, and MR properties. In this report, we present a general strategy for the synthesis of GdPO4:Pr3+ nanoparticles having new alternative modality of UV emission based on the Gd3+ ion originated from 4f7-4f7 transition, visible fluorescence due to 4f2-4f2 transition of Pr3+ ion, and magnetic property based on Gd3+ ion, which could be pot
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