The luminescence of uranium-activated tungstates and molybdates with scheelite structure

Abstract
The luminescence properties of scheelites with composition AWO4–U and AMoO4–U (A=Ca, Sr, or Ba) are reported. The red luminescence is due to a tetrahedral UO2−4 group. There is a strong vibronic coupling with low‐frequency vibrational modes. Further the frequency of the symmetric and asymmetric stretching vibrations of the UO2−4 tetrahedron have been determined. The dramatic variation of the luminescence quenching temperature with the nature of the A ion is related to the position and the width of higher excited charge‐transfer transitions. The radiant decay times are rather short (10–20 μs). Their temperature dependence shows that at least four energy levels are involved in the radiative emission processes. The green luminescence can be ascribed to the presence of a second phase of composition AUO4.

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