Photorefractive effect in doped Pb5Ge3O11 and in (Pb1−xBax)5Ge3O11

The photorefractive effect is studied in ferroelectric lead germanate crystals Pb5Ge3O11, including undoped, Fe- and Rh-doped crystals, as well as (Pb1−xBax)5Ge3O11 solid solutions. Two kinds of processes are involved in photorefractive interactions: a fast response with a time constant generally less than 1 s and the formation of slow gratings with time constants of several hours for intensities in the range of 1–30 kW/m2. Basic photorefractive parameters corresponding to the fast response, such as dark- and photoconductivities, the sign of the main charges involved in the transport process, effective trap densities, and activation energies are determined. Compared to theoretical predictions the measured effects are too small which is attributed mainly to electron-hole competition.