Synthesis and properties of Ca3Ga2Ge3O12:Tb3+ garnet phosphor

A Tb3+-activated Ca3Ga2Ge3O12 (CGGG:Tb3+ garnet phosphor was synthesized by the solid-state reaction and subsequent calcination at T-c = 800-1200 degrees C in air. The effects of the Tb3+ 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 Tb3+ can be substituted for the dodecahedral Ca2+ site, octahedral Ga3+ site, or tetragonal Ge4+ site in the CGGG host. The XRD data suggested that Tb3+ dopant prefers to occupy the octahedral Ga3+ site (Ca3Ga2(1-x)Tb2xGe3O12). The strongest Tb3+ emission was observed for the sample synthesized with x similar to 0.05. An exponential dependence was inferred from the XRD and PL intensities vs 1/T-c plots, yielding E-a similar to 3.5 eV for the CGGG lattice formation and an activation of Tb3+ in the CGGG host. PL excitation and decay characteristics showed that an energy transfer occurs from the native defect state of similar to 0.5 eV below the conduction band, via the D-5(3) state, to the D-5(4) emitting excitation state in the CGGG:Tb3+ 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.