Study of the luminescence of Eu2+ and Eu3+ states in Ca3Ga2Ge3O12:Eu garnet using synchrotron radiation excitation

The work is dedicated to the investigation of $Eu²⁺$ and $Eu³⁺$ luminescence centers in the $Ca_3Ga_2Ge_3O₁₂$ garnet using synchrotron radiation excitation. The luminescence of $Eu²⁺$ and $Eu³⁺$ states was observed in the emission spectra of $Ca_3Ga_2Ge_3O₁₂$:Eu ceramics under excitation with energies in the exciton range and the range above band gap of this garnet. The luminescence of $Eu²⁺$ ions $Ca_3Ga_2Ge_3O₁₂$ host is observed in the band peaked at 450–460 nm with decay time in the ten ns range and excited in the two wide bands peaked at 5.04 and 6.05 eV, related to the allowed 4f-5d transitions of $Eu²⁺$ ions. The $Eu³⁺$ luminescence can be excited via the $Eu²⁺$ luminescence. We have also found the energies of formation of excitons bound with $Eu²⁺$ and $Eu³⁺$ ions in Ca3Ga2Ge3O12, being equal to 7.64 and 6.95 eV, respectively, and the onset of interband transitions in this garnet which is equal to 7.83 eV at 8 K. Strong increase of the luminescence intensity of $Eu²⁺$ and $Eu³⁺$ centers is observed under excitation above 21 eV due to multiplication of electronic excitation in $Ca_3Ga_2Ge_3O₁₂$ host.