First observation of intra-5f fluorescence from an actinyl center: Np(VI) near-IR emission in Cs2U(Np)O2Cl4

The neptunyl tetrachloride ion luminesces in the near-infrared at room temperature following excitation at 628.3 or 633 nm. The emission originates from an excited state approximately 6890 cm−1 above the ground state with a lifetime of 20 μs.