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{sub B}). For T{sub B}=15 K, but not for T{sub B}=2.2 K, a significant rotation of Cresyl Violet is indicated. The broad, tailing antihole is observed to depend on T{sub 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{sub 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. {bold 141}, 447 (1990)) as well as other models.