Design and improve of the near-infrared phosphor by adjusting the energy levels or constructing new defects

Ca3Ga2Ge4O14:Cr3+ phosphors with a broad emission band are prepared by the high temperature solid state method. The emission peak position of Ca3Ga(2-x)Ge4O14:Cr3+ is located at 745 nm. Considering that the biological detection needs a widely spectra matching with the first biological window (650 nm-900 nm), Al3+ and In3+ are introduced into the Ga3+ sites to tune the peak position. When the Ga3+ (0.62 angstrom) is substituted by smaller Al3+ (0.535 angstrom), the crystal field around Cr3+ is enhanced, the energy level T-4(2)(F-4) will move up and overlap with E-2((2)G) level. As a result, the emission peak of Cr3+ shift from 745 nm to 730 nm with an enhancement in the intensity about 19 times due to the electro transfer from E-2((2)G) level to T-4(2)(F-4) level. However, the energy level T-4(2)(F-4) will move down when the Ga3+ is replaced by the larger In3+ (0.8 angstrom), which leads to the red shift of the emission peak from 745 nm to 780 nm. Meanwhile, the intensity is enhanced about 17 times with constructing the defects. In summary, the wide emission spectra of these samples can be tuned from730nm to 780 nm continuously by controlling the concentration of Al3+ and In3+. (C) 2019 Elsevier B.V. All rights reserved.