Curium: A radioactive actinide with atomic symbol Cm, atomic number 96, and atomic weight 247. Thirteen curium isotopes have been produced with mass numbers ranging from 238-250. Its valence can be +3 or +4. It is intensely radioactive and decays by alpha-emission.Actinoid Series Elements: A series of radioactive elements from ACTINIUM, atomic number 89, to and including LAWRENCIUM, atomic number 103.Luminescence: Emission of LIGHT when ELECTRONS return to the electronic ground state from an excited state and lose the energy as PHOTONS. It is sometimes called cool light in contrast to INCANDESCENCE. LUMINESCENT MEASUREMENTS take advantage of this type of light emitted from LUMINESCENT AGENTS.