The synthesis of rare-earth doped Lu₄Hf₃O₁₂ phosphor nanopowders was achieved through the combustion of metal–organic acetate–citrate amorphous gels. Their crystalline structure and morphology have been characterized by X-ray diffraction and electron microscopy. Under UV and X-ray excitation a bright luminescence of the Eu³⁺ and Tb³⁺ dopant ions has been monitored by photo-luminescence as well as by radio-luminescence measurements. We highlight the role of the formation of nanosized precursor gels as an intermediate stage in the synthesis of high-density rare-earth doped Lu₄Hf₃O₁₂ luminescent nanopowders.