1. J. Teichmann and K. Szymborski in The History of Solid-State Physics, L. Hoddeson, E. Braun, J. Teichmann, and S. Weart, eds., Oxford University Press, 1990, Chap. 4.
2. G. Baldacchini in Advances in Nonradiative Processes in Solids, B. Di Bartolo ed., Plenum Press, 1991, p. 219.
3. G. Baldacchini in Luminescence: Phenomena, Materials, and Devices, R.P. Rao, ed., Nova Science Publishers Inc., 1991, p.
4. F. Agullo-Lopez, C.R.A. Catlow and P.D. Townsend, Point Defects in Materials, Academic Press, London, 1988.
5. W.B. Fowler in Physics of Color Centers, W.B. Fowler, ed, Academic Press, New York, 1968, Chap. 2.