The lanthanoid-containing fine particles of an inorganic material, the wavelength conversion of the

The present invention aims to provide a lanthanoid-containing inorganic material fine particle that enables achievement of high luminous efficiency with less energy outflow upon conversion of the wavelength of light to a shorter wavelength. The present invention can also provide a wavelength conversion ink capable of maintaining a high emission intensity at the time of wavelength conversion for a long period of time, having high water repellency, and capable of forming a printing pattern excellent in retention properties, a coated article produced using the wavelength conversion ink, and a determination apparatus. The present invention relates to a lanthanoid-containing inorganic material fine particle having a function of converting a wavelength of light to a shorter wavelength, the lanthanoid-containing inorganic material fine particle including : a core particle; and a shell layer, the core particle containing a lanthanoid having a light-absorbing function and a lanthanoid having a light-emitting function, the shell layer including at least an outer shell containing a rare earth element, the total amount of the lanthanoid having a light-absorbing function and the lanthanoid having a light-emitting function in the outer shell being 2 mol% or less based on the amount of the rare earth element contained in the outer shell, the outer shell having a thickness of 2 to 20 nm, the core particle and the shell layer having no interface at a contact face to form a continuous body.