Physical models for the photoferroelectric phenomena

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Abstract
Photoferroelectricity is a new field which combines the photoelectric and ferroelectric phenomena.Different photoferroelectric processes can occur in pure, doped (compensated or uncompensated), semiconducting, partially ordered, polarized states. The relevant models are deduced and their application to photonic systems is discussed.The photoeffect of an incident photon flux is primarily a change in a vibronic quantum number of the absorbing species. Following this change several localized or delocalized couplings could be modified in ferroelectrics: e.g. the electron-phonon interaction, the deformation-potential modulation, the electron-order parameter fluctuation coupling, the electronion interaction.A set of “photoferroelectric” models is derived from these photoinduced couplings: the photoexcited ion model (Frank-Condon coupling), the photo-ferropolaron, the pseudo-Jahn-Teller optical centre (local vibrational hybridization), the Jahn-Teller optical centre, the Glass model (a polar character for the electron transfer probability), the Fridkin model (a new photofluctuon concept), the photo-thermoelectret and the photo-ferroelectret states.These photoferroelectric models can be handled to get a unified picture of the effect of illumination with hy larger than the bandgap on vibronic systems (photorefractive process, photoinduced Rayleigh scattering, photo-thermostimulated currents …). They can be also a proper tool in the fields of photonics and applied optics.