Reported blue upconversion from U4+ doped into Cs2ZrCl6 single crystals under green laser excitation Original Research Article

The reported blue upconversion under green argon ion laser excitation for U4+ doped into Cs2ZrCl6 has been reinvestigated. The emission is reassigned to that from the uranyl ion, by reference to the 300 K spectra of Cs2ZrCl6: UO22+ and Cs2UO2Cl4, and a detailed interpretation is given. The contamination of samples of Cs2ZrCl6: UO22+ by U4+ does not produce spectral changes of the low temperature uranyl luminescence in the range 500–600 nm.