Towards enhancement of energy transfer efficiency to Ce3+ in Gd3(Al,Ga,Sc)5O12:Ce crystals

Gadolinium aluminum gallium garnets doped with Ce ions are perspective scintillating materials with high light yield and radiation resistance. Modification of the atomic composition of the garnet by partial substitution of aluminum and gallium with scandium allows the formation of additional energy transfer channels to Ce³⁺ thus potentially improving the scintillation performance of the garnets. In the paper, the features of excitation energy transfer to the Ce³⁺ and Gd³⁺ emission centers in (Gd,Ce)₃Al_2.22Ga_2.78O₁₂ and (Gd,Ce)₃Sc_1.38Al_0.96Ga_2.66O₁₂ crystals were studied. Analysis of the reflection and luminescence excitation spectra demonstrated that partial substitution of aluminum and gallium with scandium results in the decrease of the bandgap. It was shown that the relative intensities of Ce³⁺ and Gd³⁺ emission depend on the excitation energy that is related to the competition between energy transfer channels of different origins. The analysis of luminescence excitation spectra demonstrated that 3d states of Sc participate in the formation of the conduction band bottom thus influencing the energy relaxation and energy transfer processes in the garnets. In particular, it allows the creation of scandium charge transfer excitons, which act as an additional energy transfer channel to Ce³⁺ ions that suppress the energy transfer to Gd³⁺ and enhance the relative intensity of the Ce³⁺ luminescence at low temperatures. It is concluded that the partial substitution of aluminum and gallium with scandium enhances the efficiency of the conversion of the primary hot charge carriers into secondary thermalized excitations and their transfer to dopant Ce³⁺ ions.