1. J. B. Birks and J. C. Conte, Proc. Roy. Soc,A303, 85 (1968).
2. L. M. Kutsyna and O. I. Glushchuk, Zh. Prikl. Spektrosk.,18, 888 (1973).
3. O. I. Andryushchenko and L. M. Kutsyna, in: Single Crystals, Scintillators, and Organic Luminophors [in Russian], No. 2, Khar'kov (1973), p. 123.
4. L. M. Kutsyna and O. I. Andryushchenko, Zh. Prikl. Spektrosk.,22, 332 (1975).
5. C. R. Goldschmidt, J. Tomkirwicz, and A. Weinreb, Spectr. Acta,25A, 1471 (1969).