1. B. V. Mill’, A. V. Butashin, A. M. Ellern, and A. A. Maier, Izv. Akad. Nauk SSSR, Neorg. Mater. 17 (9), 1648 (1981).
2. E. L. Belokoneva and N. V. Belov, Dokl. Akad. Nauk SSSR, 260 (6), 1363 (1981).
3. A. A. Kaminskii, B. V. Mill’, and S. E. Sarkisov, Physics and Spectroscopy Laser Crystals, Ed. by A. A. Kaminskii (Nauka, Moscow, 1986) [in Russian], p. 197.
4. O. A. Baturina, B. N. Grechushnikov, A. A. Kaminskii, et al., Kristallografiya 32 (2), 406 (1987).
5. B. V. Mill and Yu. V. Pisarevsky, Proc. IEEE/EIA Intern. Frequency Control Symp., Kansas City, Missouru, USA, 2000, p. 133.