1. F. Pellé, S. Ivanova, and J. F. Guillemoles, EPJ Photovolt. 2, 20601 (2011).
2. F. Auzel, Chem. Rev. 104, 139 (2004).
3. V. V. Ovsyankin and P. P. Feofilov, Opt. Spektrosk. 20, 526 (1966).
4. P. P. Feofilov and V. V. Ovsyankin, Appl. Opt. 6, 1828 (1967).
5. V. V. Ovsyankin and P. P. Feofilov, in Luminescence of Crystals, Molecules, and Solutions, Ed. by F. Williams (Plenum Press, New York, 1973), p. 64.