Energy-transfer processes in ${\mathrm{Cs}}_2$U${\mathrm{O}}_2$${\mathrm{Br}}_4$ crystals

The energy-transfer processes in ${\mathrm{Cs}}_2$U${\mathrm{O}}_2$ ${\mathrm{Br}}_4$ have been investigated. The emission and excitation spectra as well as the quantum efficiency and the decay of the luminescence were measured between 1.5 and 25 K with the use of selective excitation techniques. The results show that luminescence of ${\mathrm{Cs}}_2$U${\mathrm{O}}_2$ ${\mathrm{Br}}_4$ at low temperatures originates mainly from traps. For the trap with the dominant emission the concentration is determined to be about 100 ppm. On the basis of the experimental results possible models for the energy transfer in ${\mathrm{Cs}}_2$U${\mathrm{O}}_2$ ${\mathrm{Br}}_4$ are discussed. Finally, the energy-transfer processes in ${\mathrm{Cs}}_2$U${\mathrm{O}}_2$ ${\mathrm{Br}}_4$ are compared with those in uranates and ${\mathrm{Cs}}_2$U${\mathrm{O}}_2$ ${\mathrm{Cl}}_4$.