1. Rare-Earth Doped Semiconductors, edited by G. S. Pomrenke, P. B. Klein, and D. W. Langer (Materials Research Society, Pittsburgh, 1993).
2. Rare-Earth Doped Semiconductors II, edited by S. Coffa, A. Polman, and R. N. Schwartz (Materials Research Society, Pittsburgh, 1996).
3. C. Kittel, Introduction to Solid-State Physics (Wiley, New York, 1956; Nauka, Moscow, 1978), Table 3.1.
4. J. E. Colon, D. W. Elsaesser, Y. K. Yeo, R. L. Hengehold, and G. S. Pomrenke, Rare-Earth Doped Semiconductors, edited by G. S. Pomrenke, P. B. Klein, and D. W. Langer (Materials Research Society, Pittsburgh, 1993)in Ref. 1, p. 251.
5. T. Zhang, J. Sun, N. V. Edwards, D. E. Moxey, R. M. Kolbas, and P. J. Caldwell, Rare-Earth Doped Semiconductors, edited by G. S. Pomrenke, P. B. Klein, and D. W. Langer (Materials Research Society, Pittsburgh, 1993)in Ref. 1, p. 257.