Optical spectroscopy of Np4+ (5f3) ion diluted in ThSiO4 and ThO2 crystalline hosts

The absorption and emission spectra of Np4+ in ThSiO4 and ThO2 have been recorded at 4.2 K in the energy range 4000-25000 cm-1. For ThSiO4:Np4+, 29 levels are assigned in the D2d crystal field symmetry and fitted with a least-squares routine leading to a r.m.s. of 45 cm-1. The values of the spectroscopic parameters are: F2=45212, F4=38018, F6=28345, ζ=2129, B02=333, B04=1515, B44=-3563, B06=-1853 and B46=-802 cm-1. For ThO2, a preliminary interpretation is given on the basis of the ThSiO4 results. (orig.)