Vol. 87 (1995) ACTA PHY SICA POLONICA A No. 1 Proceedings of the XXIII International School of Semiconducting Compounds, Jaszowiec 1994 ROOM AND LIQUID NITROGEN TEMPERATURE REFLECTIVITY SPECTRA OF Ζn1- x Cο x Se MIXED CRYSTALS* D. DĘBOWSKA, M. ZIMNAL-STARNAWSKA, A. KISIEL Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland M. PIACENTINI Dipartimento di Energetica, Universita'degli Studi di Roma via A. Scarpa 14, 00161 Roma, Italy N. ZEMA, F. LAMA Istituto di Struttura della Materia del CNR, via E. Fermi 38, 00044 Frascati, Italy AND W. GIRIAT IVIC Centro di Fisica, Caracas, Apartado 21 827, Venezuela The optical properties of the semiconducting compounds Ζn1-xCox Se crystallizing in the zinc-blende structure have been investigated. The reflec- tivity spectra of these materials for dicherent concentration of Co ions, have been taken out in a wide energy range between 4 and 25 eV at room (RT) and liquid nitrogen temperature (LNT) using synchrotron radiation from ADONE Storage Ring in Frascati. The comparisons between the reflectivity spectra of ternary systems and host crystal ZnSe are made. On the basis of the experimental and theoretical results, the changes of the structures of the reflectivity spectra of host crystal ZnSe caused by the influence of transition metal ions are discussed. PACS numbers: 78.20.-e The ternary compounds Zn 1-xCoxSe belong to the group of materials known as diluted magnetic semiconduction (DMSs), in which the transition metal ions (Mn, Fe, Co) randomly replace some of cations (Zn, Hg, Cd) in the II-VI semicon- ductor lattice. Due to their important semiconducting as well as magnetic prop- erties, DMSs have been the subject of extensive studies [1]. While the intrinsic This work partially supported in the framework of the project no. PB 931/2/91 in the years 1991-94 by the State Committee for Scientific Research (Republic of Poland) and by Consorzio Italian INFM and CNR through the GNSM. (275)