Application of non-photochemical hole burning to the two-photon spectroscopy of impurity molecules in low temperature glasses

Electron–phonon coupling in two-photon spectral gratings: role of molecular symmetry

“…Intuitively, this effect implies the presence of narrow zero-phonon lines (ZPL) in TPA transition. TPA pure electronic ZPLs were shown for several molecules, including centrosymmetric [4][5][6][7][8][9][10] and non-centrosymmetric ones [11,12].…”