Luminescence quantum yield and multiplication of electronic excitations in the corundum crystals V. V. Harutunyan, T. S. Hakobyan, V. A. Gevorkyan and V. N. Makhov Eur. Phys. J. B, 12 1 (1999) 31-33 Published online: 15 November 1999 DOI: 10.1007/s100510050972