| abstract |
(57) Abstract: (modified with) Disclosed is useful as a clear, colorless ink material, to provide a Yb PO 4 and substituted rare earth phosphate and its production process and the ink having a high infrared absorptivity. SOLUTION: The average particle size is 0.1 to 5 μm, and the crystallite is 20 to 40. nm, the molar ratio of P / Yb is 1.08 to 2.0, and the wavelength is 975 to 977. An infrared absorbing material comprising ytterbium phosphate or a substituted rare earth phosphate having an infrared absorptance at 60 nm or more, and an aqueous solution of Yb salt or substituted rare earth salt and an aqueous solution of phosphoric acid are combined with phosphorus / (Yb or substituted rare earth) Is reacted at a molar ratio of 1.2 to 6.0 at a temperature of 50 to 100 ° C., the product is separated and calcined at 300 to 1100 ° C. for 2 to 15 hours. |