Abstract: This invention provides a novel bioimaging technique that can achieve a deep observation depth and a novel method for marking a lesion that allows clear recognition of the lesion from outside a living body. This invention also provides a bioimaging marker comprising a fluorescent material obtained by doping a ceramic with rare earths and the like and a bioimaging technique comprising detecting near-infrared fluorescence that can sufficiently penetrate a living body generated upon excitation of the marker with near-infrared excitation light.