K. K. Rebane, «Purely electronic zero-phonon line as the foundation stone for high-resolution matrix spectroscopy, single-impurity-molecule spectroscopy, and persistent spectral hole burning. Recent developments: Spectroscopy in Cryocrystals and Matrices», Fiz. Nizk. Temp., вип. 29, вип. 9-10, с. 1101–1108, Вер 2003.