Near Infrared YVO 4 :Nd,Yb Nano Phosphor Synthesized By Microreaction Method for In Vivo Bioimaging

Over past few years, nano phosphors have been attracting attention as candidate materials for in vivo biological imaging, and several types of phosphor material have been investigated. Organic phosphor materials have an excellent luminescent efficiency, however their protein has a discoloration problem during the observation. Semiconductor quantum dot phosphors also have a problem in practice, that is, it contains harmful elements in a human body. Therefore, the development of highly stable and harmless phosphors are desired.[1]An ultraviolet (UV) light, which is usually used for exciting both organic fluorescent materials and semiconductor quantum dot phosphors, damages the human body. In addition, it is hard to observe deep part of a human body by using a UV light. To solve these problems, it is effective to use a high bio-permeability near-infrared region (so called biological window).[2] Therefore, the phosphors having the excitation and emission band in a near-infrared region must be developed. The particle size of 30 - 200 nm is also needed for drug delivery system. [3]We previously reported the synthesis of the nano phosphor materials synthesized by the microreaction (MR) method, which is one of the solution synthesis methods. [4] The MR method has an advantage to perform a homogeneous reaction and to precisely control the reaction conditions such as temperature and pH. A higher quantum efficiency has been obtained by MR method compared to the traditional solution synthesis. [5] In this study, we pay attention to YVO 4 :Nd,Yb as the vivo bioimaging nano phosphor. The pH value and temperature during the MR synthesis have been varied, and the relation between these reaction parameters and luminescent properties has been investigated.The precursor of YVO 4 :Nd,Yb was prepared by a citric-acid-gel method using the MR system. The MR system consists of liquid sources, syringe pumps, a mixer cell, a mixing/reaction tube, and an auto-sampler. The 1-mm-width T-branch channel was used as the mixer cell. The cell was prepared by a sandblasting method with glass substrates. A pH sensor was placed at the outlet of the mixer cell. Y(CH 3 COO) 3 ·4H 2 O, Nd(CH 3 COO) 3 ·H 2 O, Yb(CH 3 COO) 3 ·4H 2 O and C 6 H 5 Na 3 O 7 ·2H 2 O was used as the acid source (pH=5). Na 3 VO 4 and NaOH were used as the basic solution (pH=12) sources. These two sources were mixed at the T-branch mixer, and the mixture solution was passed through a Teflon tube (1000μm diameter) in an ul