Control of Nd and Cr concentrations in Nd,Cr : Gd3Ga5O12 single crystals grown by Czochralski method

During the growth process of the Nd,Cr:Gd3Ga5O12 (Nd,Cr:GGG) laser crystals the optimum concentrations of the dopants cannot be realized in axial dire ction of the crystal at a constant pulling (growth) rate as the effective s egregation coefficients (k) of Nd3+ and Cr3+ are not unity and not uniform (k < 1 and k > 1, respectively). To solve this problem the dopant concentra tions were measured in the crystals grown at different pulling rates by ato mic absorption to determine the effective and equilibrium segregation coeff icients and the ratio of the boundary layer thickness and diffusion coeffic ients. In the light of these parameters we suggest a pulling (growth) rate program as a function of the fraction of the crystallized melt leading to t he smallest concentration variation of the dopants along the length axis of the crystals. The variation of Nd3+ concentration in the crystal reduced f rom 35% to 19% while the laser efficiency increased by 15-20% by this metho d. (C) 2001 Elsevier Science B.V. All rights reserved.