Excitation Energy Dependence in Near-infrared Photoluminescence Spectra and Dynamics of PuO_2~(2+) in Cs_2U(Pu)O_2Cl_4

摘要

Recently we reported the observation of near-infrared photoluminescence from metal-centered 5f electronic excited states of PuO_2~(2+) doped into polycrystalline Cs_2U(Pu)O_2Cl_4.[1] Photoluminescence dynamics following pulsed excitation show complicated decay patterns suggesting that multiple luminescent states are involved. Here we report the results of two recent sets of experiments showing that photoluminescence processes depend significantly on the energy of photoexcitation. In the first case, decay kinetics following excitation at a lower energy are missing an in-growth term that is present when exciting at higher energy. In the second case, we have observed that lower excitation energy produces significantly reduced number of emission transitions than higher excitation energy. Both observations suggest that higher energy excitation populates feeder states that decay to emitting states, causing signal from the latter to have an in-growth followed by a decay characteristic of their intrinsic lifetimes, whereas lower energy excitation leads to more direct population of luminescent states.