This paper discusses the IR absorption spectra of CsI crystals grown with an admixture of a salt of divalent europium. Crystals with a diameter of 250 mm and a height of 350 mm have been grown by a modified Kyropoulos method with replenishment by the melt, in which a crucible-supply unit of special design is used. It is shown that adding a strong reducing agent to the supply makes it possible to obtain crystals whose IR spectra contains no absorption bands of oxygen-containing anions. The europium oxide formed in the melt is deposited on the bottom of the supply unit and does not enter the growth zone. The volume absorption coefficient of such crystals at a wavelength of 10.6 µm lies within the limits (2-6)×10−4 cm−1, and this broadens the possibilities of their practical application.
A. M. Kudin, A. I. Mitichkin, T. A. Charkina, B. G. Zaslavskiĭ, S. I. Vasetskiĭ, T. P. Rebrova, Yu. A. Zagoruĭko, and P. V. Mateĭchenko, "CsI crystals for the mid-IR region," J. Opt. Technol. 74, 633-635 (2007)