The optical absorption spectra of nominally pure and Mn-doped Czochralski-grown single crystals of Mg2SiO4 have been measured from 1 eV to ~ 7.5 eV. The intensity of weak optical absorption bands at 4.78, 6.0, and 6.6 eV in the nominally pure crystal has the same dependence upon irradiation with gamma rays and subsequent thermal treatments as does the intensity of the electron paramagnetic resonance (Epr) spectrum of Fe3+ located in the forsterite M(2) site. On the basis of this correlation, it is assumed that the optical bands are due to the Fe3+ ion. Oscillator strengths, calculated on the basis of the concentration of Fe3+ ions, are 0.2, 1.0, and 0.5 for the 4.78, 6.0, and 6.6 eV bands, respectively. These strengths are those expected for charge-transfer bands. The opticalabsorption spectrum of the Mn-doped crystal has an intense band at 6.5 eV and an indication of another at>7.3 eV. If it is assumed that the 6.5 eV band is due to a transition involving Mn2+, then its oscillator strength is 0.1, and hence this band is attributed to a charge-transfer transition involving Mn2+ Tentative estimates of Dq are Dq(Fe3+) ≈ 1050 cm−1 and Dq(Mn2+) ≈850 cm−1.

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