Self-trapped state and phonon localization in TiO2 quantum dot with a dipole layer

The discrete phonon spectra of TiO2 quantum dot with a dipole layer is reported. The absorption intensities of different LO phonons are related to the phonon-electron coupling in accord with the prediction of the continuum polarization model. The two-phonon bound state appeared due to the localization effect. The optical absorption of the self-trapped state [reported in Appl. Phys. Lett. 59, 1826 (1991)] may be related to the strong electron-phonon interaction in this system, i.e., a bipolaronic state might form with the presence of surface donor.