Synthesis and properties of Ca3Ga2Ge3O12:Tb3+ garnet phosphor

Abstract A Tb 3+ -activated Ca 3 Ga 2 Ge 3 O 12 (CGGG:Tb 3+ ) garnet phosphor was synthesized by the solid-state reaction and subsequent calcination at T c = 800–1200 °C in air. The effects of the Tb 3+ activator concentration and calcination temperature on the phosphor properties were investigated using X-ray diffraction (XRD) and photoluminescence (PL) measurement techniques. There is a possibility that Tb 3+ can be substituted for the dodecahedral Ca 2+ site, octahedral Ga 3+ site, or tetragonal Ge 4+ site in the CGGG host. The XRD data suggested that Tb 3+ dopant prefers to occupy the octahedral Ga 3+ site (Ca 3 Ga 2(1− x ) Tb 2 x Ge 3 O 12 ). The strongest Tb 3+ emission was observed for the sample synthesized with x ~ 0.05. An exponential dependence was inferred from the XRD and PL intensities vs 1/ T c plots, yielding E a ∼ 3.5 eV for the CGGG lattice formation and an activation of Tb 3+ in the CGGG host. PL excitation and decay characteristics showed that an energy transfer occurs from the native defect state of ∼ 0.5 eV below the conduction band, via the 5 D 3 state, to the 5 D 4 emitting excitation state in the CGGG:Tb 3+ system. Temperature dependence of the PL intensity measured at T = 20–450 K was successfully explained by the thermal quenching of E q = 0.20 eV with considering a reservoir state of E t = 10 meV in a charge transfer process of the light emitting event.