Ultrafast Photocarrier Dynamics and Nonlinear Optical Absorption of a Layered Quaternary AgInP₂S₆ Crystal

Abstract

Layered quaternary metal thio/selenophosphates exhibit composition-dependent physical properties and have valuable applications in optoelectronic devices. Exploring their optical properties and photoexcited carrier dynamics is a prerequisite for their device design. Here, the ultrafast photocarrier dynamics and nonlinear absorption of a bulk AgInP2S6 crystal, a new member of this material family, are investigated by employing photoluminescence, time-resolved transient optical spectroscopies, and intensity-dependent transmission. The AgInP2S6 exhibits defect-assisted photoluminescence with more effective excitation under defect-state absorption and two-photon absorption at 800 nm. After initial intraband relaxation, the interband-excited carriers naturally accumulate at the conduction band minimum or valance band maximum, and then most of the nonequilibrium carriers relax via interband nonradiative recombination while the rest are transferred to the defect bands. Following that, the nonequilibrium carriers in the defect bands will first relax to the bottoms of the defect bands and finally recombine there. As compared with its analogue CuInP2S6, the substitution of Cu with Ag results in the variation of the two-photon absorption coefficient as well as the increase in carrier relaxation times due to the accompanying defect change. These findings provide microscopic insights into the optical response process of AgInP2S6 and valuable references for developing its optoelectronic devices.