Defects mediated charge disturbance in quantum-confined AgxS/AgInS2 random alloys – Toward slowly decaying quantum dot emitters

This works presents comprehensive studies on fundamental excitations trapping and the resulting charge destabilization in cubanite Ag_xS/AgInS₂ quantum-confined random alloys. The observed optical activity of defect levels, related to silver alloying, is discussed basing on the femtosecond excited time-resolved photoluminescence spectrograms as well as theoretical predictions obtained via the density functional theory within the reduced cluster model. Impact of the charge trapping on the third-order optical hyper-polarizabilities has also been investigated basing on the two-photon excitation action cross sections. It has been shown that silver induced defects in the Ag_xS/AgInS₂ random alloys are responsible for effective electron/hole trapping and strong temporal charge uncompensation. The silver on indium Ag_In, silver interstitials Ag_i and higher-order defect clusters e.g. (Ag_In^2--2Ag_i⁺) formed effectively due to defect compensation mechanism have been considered in this work as providing possible pathways of defect mediated depopulation of the excited states. The electron/hole trapping mechanism is also discussed as a major mechanism responsible for fast trionic relaxations leading to strong deviation from the first-order decay law and significant temporal red-shifts of the photoluminescence band maximum. Further, it is shown that controlling the silver alloying ratio and the resulting number of defects charge states, it is possible to cause variation of the average photoluminescence decay times by an order of magnitude. The silver alloying was also found as an efficient route for significant increase of the two-photon excitation action cross section.