Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi3GeO4 crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, gxx = gyy = 1.915, gzz = 1.932. The EPR spectrum is dictated by Cr4+ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 µm is also caused by transitions of Cr4+ with tetrahedral surroundings to germanium sites.