Complex studies of photoconductivity, two-photon absorption (TPA) and third harmonic generation (THG) were performed for three principal representatives of chalcogenide crystals. Comparison of carrier transport kinetics and third order nonlinear optical properties was performed and the principal role of the anionic co-ordination is discussed. Specific features of photoconductivity in synthesized crystals show that the relaxation kinetics of photoconductivity can be determined by the existence of at least two types of relaxation processes: slow and quick. The control of the relaxation processes for s- and r-centres was carried out by temperature dependences of t-levels relaxation photoconductivity. The maximum THG is observed for the sample AgGaGe5Se12. The less THG exists for the sample AgGaGe3Se8 and the lowest for the AgGaGe4Se10. (C) 2016 Elsevier Ltd. All rights reserved.