Disclosed is a method of non-invasive
infrared imaging, comprising (a) administering a composition containing
infrared-emitting particles which contain
rare earth elements that emit in the short-
wavelength infrared (SWIR) spectrum, where the particles are encapsulated with a biocompatible matrix to form downconverting encapsulated particles; and (b) irradiating with infrared
radiation, where both excitation and emission spectra of the encapsulated particles are in the infrared region. Analogous methods of image-guided biomedical intervention, and
drug tracking and delivery are also disclosed. Also disclosed is a composition for biomedical applications, containing infrared-emitting particles which contain
rare earth-elements that emit in the short-
wavelength infrared (SWIR) spectrum, where the particles are encapsulated with a biocompatible matrix to form downconverting encapsulated particles.