The present invention is directed α-particle emitting nanoparticles that comprise a lanthanide phosphate sequestration shell enclosing an α-emitting-radioisotope-doped lanthanide phosphate core such that the shell allows at least some of the α emissions from the α-emitting radioisotope to pass therethrough and prevents at least some radioactive decay products of the α-emitting radioisotope from exiting the α-particle emitting nanoparticle. Further, such α-particle emitting nanoparticles may be coated with gold and functionalized. Additionally, a method for making and using the same are disclosed.