1. L. G. Van Uitert, H. M. O'Bryan, M. E. Lines, H. J. Guggenheim, R. L. Barns and G. Zydzik, Mat. Res. Bull, to be published.
2. L. G. Van Uitert, H. M. O'Bryan, H. J. Guggenheim, R. L. Barns and G. Zydzik, Mat. Res. Bull, to be published.
3. M. E. Lines - private communication.
4. Oscillator strengths in tetrahedral semiconductors