Photoproduction of Long-Lived Holes and Electronic Processes in Intrinsic Electric Fields Seen through Photoinduced Absorption and Dichroism in Ca_3Ga_{2-x}Mn_xGe_3O_{12} Garnets

Abstract

Long-lived photoinduced absorption and dichroism in the Ca_3Ga_{2-x}Mn_xGe_3O_{12} garnets with x < 0.06 were examined versus temperature and pumping intensity. Unusual features of the kinetics of photoinduced phenomena are indicative of the underlying electronic processes. The comparison with the case of Ca_3Mn_2Ge_3O_{12}, explored earlier by the authors, permits one to finally establish the main common mechanisms of photoinduced absorption and dichroism caused by random electric fields of photoproduced charges (hole polarons). The rate of their diffusion and relaxation through recombination is strongly influenced by the same fields, whose large statistical straggling is responsible for a broad continuous set of relaxation components (observed in the relaxation time range from 1 to about 1000 min). For Ca_3Ga_{2-x}Mn_xGe_3O_{12}, the time and temperature dependences of photoinduced absorption and dichroism bear a strong imprint of structure imperfection increasing with x.