I. V. Legchenkova, N. B. Silaeva, V. N. Zoryansky, P. V. Zinoviev, V. V. Eremenko, A. A. Avdeenko, K. A. Yagotintsev, M. A. Strzhemechny, Yu. E. Stetsenko, A. I. Prokhvatilov, and R. S. Ruoff, Structure and photoluminescence of helium-intercalated fullerite C₆₀, Low Temp. Phys. 28, (2002) [Fiz. Nizk. Temp. 28, 1320-1323, (2002)].