Synthesis, Crystal Structure, and Enhanced Luminescence of Garnet‐Type Ca 3 Ga 2 Ge 3 O 12 :Cr 3+ by Codoping Bi 3+

Garnet‐type compound Ca 3 Ga 2 Ge 3 O 12 and Cr 3+ ‐doped or Cr 3+ /Bi 3+ codped Ca 3 Ga 2 Ge 3 O 12 phosphors were prepared by a solid‐state reaction. The crystal structure of Ca 3 Ga 2 Ge 3 O 12 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 Cr 3+ ‐doped Ca 3 Ga 2 Ge 3 O 12 sample, and the enhanced NIR PL emission intensity and LLP decay time can be realized in Cr 3+ /Bi 3+ codped samples. The optimum concentration of Cr 3+ in Ca 3 Ga 2 Ge 3 O 12 phosphor was about 6 mol%, and optimum Bi 3+ concentration induced the energy‐transfer ( ET ) process between Bi 3+ and Cr 3+ 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 Bi 3+ to Cr 3+ 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 Bi 3+ can also improve the thermal stability of the NIR emission.