Synthesis, Crystal Structure, and Enhanced Luminescence of Garnet-Type Ca3Ga2Ge3O12:Cr3+ by Codoping Bi3+

Garnet-type compound Ca3Ga2Ge3O12 and Cr3+-doped or Cr3+/Bi3+ codped Ca3Ga2Ge3O12 phosphors were prepared by a solid-state reaction. The crystal structure of Ca3Ga2Ge3O12 host was studied by X-ray diffraction (XRD) analysis and further determined by the Rietveld refinement. Near-infrared (NIR) photoluminescence (PL) and long-lasting phosphorescence (LLP) emission can be observed from the Cr3+-doped Ca3Ga2Ge3O12 sample, and the enhanced NIR PL emission intensity and LLP decay time can be realized in Cr3+/Bi3+ codped samples. The optimum concentration of Cr3+ in Ca3Ga2Ge3O12 phosphor was about 6mol%, and optimum Bi3+ concentration induced the energy-transfer (ET) process between Bi3+ and Cr3+ ions was about 30mol%. Under different excitation wavelength from 280 to 453nm, all the samples exhibit a broadband emission peaking at 739nm and the intensity of NIR emission increases owing to the ET behavior from Bi3+ to Cr3+ ions. The critical ET distance has been calculated by the concentration-quenching method. The thermally stable luminescence properties were also studied and the introduction of Bi3+ can also improve the thermal stability of the NIR emission.