Synthesis and characterization of Cr4+-doped Ca2GeO4 tunable crystal

• The growth, structure and spectral properties of Cr4+:Ca2GeO4 single crystal have been studied.
• The Raman spectral and XPS analysis show that we successfully obtained Cr4+:Ca2GeO4 single crystal.
• Fluorescence lifetime and emission cross section are up to 12 μs and 4.61 × 10−19 cm2, respectively.

The growth, structure and spectral properties of a Cr4+:Ca2GeO4 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 Cr4+:Ca2GeO4 crystal are presented in this paper. In the absorption spectra, the transitions from the 3A2 ground state to the three orbital components of the 3T1 and 3T2 excited state are observed. The range of the fluorescence spectroscopy band of the Cr4+:Ca2GeO4 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 3T2 → 3A2 transition of the Cr4+ 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 cm2, respectively.