Up-conversion and down-conversion photo-luminescence in rare earth compounds are disclosed. Broadband, super-radiant, and discrete line emissions are observed. The rare earth compounds include a rare earth element and at least one other element selected from chalcogens, halogens, nitrogen, and phosphorus. The rare earth compounds include, but are not limited to, rare earth oxides, fluorides, and oxyfluorides. Doping and co-doping of rare earth compounds in an optical host material is not required. The compounds are irradiated with incident light having an incident wavelength that is selected to be highly absorbed by the rare earth compound. The up-conversion and down-conversion luminescence have been observed which may be caused by unknown electron transitions, particularly in the case of ytterbia.