Absorption and luminescence spectroscopy of Cr4+-doped Ca2GeO4. A potential near infrared laser material

Near infrared (NIR) absorption and luminescence experiments on Cr4+-doped Ca2GeO4 single crystals are reported. In the absorption spectra three transitions from the 3A2 ground state to the three orbital components of the 3T2 excited state are observed. The luminescence transition is from the lowest of these three orbital components to the ground state. Although the luminescence transition is spin allowed it is characterized by an unusually small Huang-Rhys factor. The luminescence of Cr4+-doped Ca2GeO4 is considerably less quenched at 275 K than the luminescence of the well-known NIR laser material Cr4+-doped forsterite.