Phase formation and characterization of Sr3Y2Ge3O12, Sr3In2Ge3O12, and Ca3Ga2Ge3O12 doped by trivalent europium

This work reports on the phase formation during a solid-state reaction of Eu³⁺-doped garnets with the general formula A₃B₂Ge₃O₁₂ (A=Ca, Sr and B=Ga, In, Y) and their luminescent properties. It is shown by XRD and DTA/TG experiments that the garnet-phase formation is completed at 1100-1200 °C. Moreover, it turned out that the position of the oxygen to europium charge-transfer band and the intensity of the forbidden 4f-4f transitions of Eu³⁺ is dependent on the covalent interaction between the Eu³⁺ activator and the surrounding oxygen anions. The investigated red-emitting luminescent materials show high lumen equivalents and deep red emission at the same time, which makes them attractive for the application in LEDs (light emitting diodes), in particular for near UV-emitting LEDs.