噴霧乾燥法による近赤外励起希土類添加LaOClナノ蛍光体の作製

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  • Fabrication of rare-earth-doped LaOCl nanophosphors by using spray dryer

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<p>Fluorescence bioimaging is a technique to visualize biological phenomena both in vivo and in vitro by specific adsorption of fluorescence probes to target organic tissues. One of the most serious problems in the fluorescence bioimaging is the limitation of observation time due to color-fading of the organic fluorescence probes and damages on the bio system, both of which are caused by the excitation of ultraviolet irradiation. This problem will be solved by using upconversion emission of rare-earth doped inorganic nanophosphors under infrared excitation. For the practical application of inorganic phosphors by using upconversion emission of doped rare earth, it is essential to choose an appropriate matrix with a low maximum phonon energy for efficient emissions and practical chemical durability. It is also important to prepare the phosphors in small particle-sizes with nanometer-order to probe micrometer-order cells. Lanthanum oxyhalides (LaOCl), as an intermediate host between oxides and halides, have both moderate phonon energy and chemical durability. LaOCl nanoparticles containing trivalent erbium ions (Er3+) are prepared through a self-hydrolysis process of hydrated chlorides of lanthanum (LaCl3) and erbium. However, this process costs much time ～12h to dry LaCl3 aqueous solution. In this study, the acceleration of this process was demonstrated by using a spray dryer. The powder prepared by spray drying of Er3+ doped LaCl3 aqueous solution was calcined at 700 ℃ in air and nitrogen (N2) atmospheres. The samples after calcination were evaluated by fluorescence emission, X-ray diffraction, and dynamic laser scattering. X-ray diffraction measurement showed that the sample after calcination in a N2 atmosphere contained LaOCl nanoparticles in LaCl3 matrix. Dynamic laser scattering measurement showed that the average particle size of LaOCl was about 600 nm. The Er3+ doped LaOCl nanoparticles showed visible upconversion emission around 500 and 660 nm after calcination under excitation at 980 nm. It was shown that rare-earth doped LaOCl nano phosphor was prepared by spray drying followed by calcination in a N2 atmosphere.</p>

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