A Verification of the Occurrence of the Downconversion Effect (Transformation of a Quantum of VUV Radiation into Two Photons of Luminescence in the Visible Range) in KGd_2F_7 and K_2GdF_5 Crystals Doped with Tb~(3+) Ions

摘要

In order to verify whether the downconversion mechanism can occur in KGd_2F_7 and K_2GdF_5 crystals, which contain different concentrations of Tb~(3+) ions, we have investigated the emission and luminescence-excitation spectra of these crystals. Our experimental results have not shown the occurrence of the downconversion effect in the examined crystals, since the rate of nonradiative relaxation from upper 4f5d levels to lower-lying 4f5d- and 4f levels of the Tb~(3+) ion is likely to exceed the rate of possible cross relaxation from these high-lying 4f5d levels with energy transfer to neighboring Tb~(3+) ions.