Synthesis and characterization of Cr4+-doped Ca2GeO4 tunable crystal

Abstract The growth, structure and spectral properties of a Cr 4+ :Ca 2 GeO 4 single crystal have been reported in this paper. XPS analysis demonstrated that the chromium in the single crystal is tetravalent; this is further confirmed by fluorescence spectroscopy. The near-infrared, visible absorption and near-infrared luminescence spectrum of the Cr 4+ :Ca 2 GeO 4 crystal are presented in this paper. In the absorption spectra, the transitions from the 3 A 2 ground state to the three orbital components of the 3 T 1 and 3 T 2 excited state are observed. The range of the fluorescence spectroscopy band of the Cr 4+ :Ca 2 GeO 4 crystal at room temperature is from 1000 nm to 1600 nm. The single band with a maximum peak at 1317 nm at room temperature is attributed to the 3 T 2  →  3 A 2 transition of the Cr 4+ ions. The FWHM of the fluorescence spectrum is 201.19 nm, and the fluorescence lifetime and emission cross section are up to 12 μs and 4.61 × 10 − 19  cm 2 , respectively.