SEGREGATION OF Ce IMPURITIES IN KMgF₃ SINGLE CRYSTALS. O. Bouzanov^*, M. D' Elena, C. Sanipoli, A. Scacco, Dipartimento di Fisica, Universita La Sapienza, P. le A. Moro 2, 00185 Roma, Italy

Effects of impurity segregation in the growth of single crystals from the melt have been quantitatively determined in several ionic systems. In general, evaluation of segregation coefficients is experimentally achieved by measuring with appropriate techniques the distribution along the growth direction of the dopant species and making use of, the normal freeze equation. No satisfactory information has been obtained up to now about segregation of impurities in the growth of single crystals of perovskite-like compounds, which turned out recently to be attractive as active media for solid state laser or radiation dosimetry applications. In this work, results concerning the segregation of Ce impurities in the growth of KMgF₃ crystals are reported. All samples were obtained from the melt with the Czochralski method by using Pt crucibles in an inert atmosphere. A very detailed study has been carried out on the distribution of the dopant, added as CeF₃ to the melt formed by stoichiometric mixtures of KF and MgF₂, as a function of the growth rate and of the initial concentration in the liquid phase. The impurity concentration has been determined from the measurements of the optical absorption spectra in the ultra-violet region. Tha data show that the dopant concentration increases with the grown volume in all crystals, indicating for the effective segregation coefficient a value lower than 1. A quantitative determination of such a value is under way.

^*Permanent address: Moscow Steel and Alloys Institute, Leninski Prosp. 4, 117936 Moscow, Russia