1. A survey of color center physics as known in its prime can be found in: W. B. Fowler (ed.): Physics of color center ( Academic, New York 1968 )
2. For an extensive survey of the physics of laser-active color centers, see L. F. Mollenauer: “Color Center Lasers” in The Laser Handbook ed. by M. Stitch, M. Bass (North Holland, Amsterdam 1985) Chap. 3
3. L. F. Mollenauer: “Color Center Lasers”, in Quantum Electronics,Part B ed. by C. L. Tang (Academic, New York 1979) Chap. 6 (This is considerably earlier and less up-to-date than 16.21.)
4. B. Henderson: Opt. Lett. 6, 437 (1981)
5. L. F. Mollenauer, D. M. Bloom: Opt. Lett. 4, 247 (1979)