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 6 mol%, and optimum Bi3+ concentration induced the energy‐transfer (ET) process between Bi3+ and Cr3+ ions was about 30 mol%. Under different excitation wavelength from 280 to 453 nm, all the samples exhibit a broadband emission peaking at 739 nm 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.