MECHANISM OF NONPHOTOCHEMICAL HOLE BURNING - CRESYL VIOLET IN POLYVINYL-ALCOHOL FILMS

Polarized nonphotochemical hole-burned spectra of Cresyl Violet in polyvinyl alcohol films are presented for various burn temperatures (T(B)). For T(B) = 15 K, but not for T(B) = 2.2 K, a significant rotation of Cresyl Violet is indicated. The broad, tailing antihole is observed to depend on T(B). The quantum efficiency distributions for the zero-phonon hole and pseudo-phonon sideband are quite similar, proving that the phonons created by excitation of the phonon sideband are not important for hole burning. The quantum efficiency is independent of T(B) over the range studied, 1.6-15 K. Over this range essentially 100% of the zero-phonon lines can be burned. The results show that the standard two-level-system (extrinsic) model for nonphotochemical hole burning is inadequate. The results are discussed in terms of an outside-in hierarchy of configurational relaxation events model [Chem. Phys. 141, 447 (1990)] as well as other models.