Optical, magneto-optical and EPR study of chromium impurities in Bi4Ge3O12 single crystal

Abstract The spectroscopic properties of Cr impurities in four Bi 4 Ge 3 O 12 single crystals of different origins have been investigated in detail with three complementary techniques. Optical absorption, electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) demonstrate that Cr 4+ at the tetrahedral germanium site is by far the dominant species in these crystals. Low temperature MCD is shown to be appropriate for a nondestructive evaluation of the amount of dopant. Lattice defects appear to be present in as-grown crystals. Diamagnetic centers, contributing to the near-u.v. absorption, are also formed by u.v. irradiation at 310 nm. Finally X-ray irradiation at 15 K produces similar but more drastic effects on the absorption spectra.