Upconversion Fluorescent Materials Studies to Lead the Development of Near Infrared Biophotonics

: Studies on up-conversion (UC) fluorescent materials are closely related to the emergence of materials that exhibit UC fluorescence and the development of their synthetic processes, and is also an opportunity to develop biophotonics using near-infrared light as excitation light, which has been at-tracting attention in recent years. The basis of the design of a fluorescent material is how to emit the given excitation energy as light without converting it into heat. The establishment of a method for synthesizing fluoride nanoparticles had a great influence on the development of UC fluorescent materials for biophotonics, and once a stable method for synthesizing nanoparticles is established, the design and synthesis of organic-inorganic composites using them had broken out. An important guideline in this case is again how to avoid the heat generation. It was inevitable to consider the effect of organic molecules, which have not been discussed so far, on the thermal relaxation of the excited electrons of rare earth ions in ceramic nanoparticles. This paper introduces the development of biophotonics, which originated from the studies on UC fluorescent materials, and presents the concept of the influence of organic molecular systems on electrons of rare earth ions in inorganic nanoparticles.