Effect of melt non-stoichiometry on chromium entry into Cr:Mg2SiO4 crystals

The study of chromium doped forsterite Cr:Mg2SiO4 laser crystals grown from non-stoichiometric melts has been accomplished. Concentration series of the crystals were grown by Czochralski technique from the melts with different MgO/SiO2 molar ratios. The unit cell parameters of the crystals and their hydrostatic densities were measured, and the actual molar weights of the samples were calculated. Both the revealed hydrostatic densities and the actual molar weights appeared to be essentially less than the corresponding values for the stoichiometric Mg2SiO4. Cr4+ content in the crystals, acquired from the optical absorption spectra, linearly increases with increment of MgO excess in the parent melt within whole studied compositions range, whereas the increment of Cr3+ in the same crystals comes to the saturation. This difference in the Cr4+ and Cr3+ behavior opens the potential possibility to optimize the Cr4+/Cr3+ concentrations ratio and to improve in the future lasing properties of the crystals.