1. G. Blasse, editor, Mat. Res. Bull. 16, 3–4 (1987).
2. R.G. Papalardo, in Spectroscopy of Solid-State Laser-type Materials (Ed. B. Di Bartolo ), Plenum Press, New York, 1987, p. 397.
3. See e.g. G. Blasse, in Radiationless Processes (Ed. B. Di Bartolo ), Plenum Press, New York, 1980, p. 287.
4. H.S. Kiliaan, J.F.A.K. Kotte and G. Blasse, J. Electrochem. Soc. 134, 2359 (1987).
5. D. Curie, in Optical Properties of Ions in Solids (Ed. B. Di Bartolo ), Plenum Press, New York, 1975, p. 71.