Ultra-High Nonlinear Saturable Absorption Responses and Ultra-Fast Carrier Dynamics of Organic DAST

摘要

Third-order nonlinear optical (NLO) absorption properties and ultra-fastcarrier dynamics of organic 4-N,N-dimethylamino-4’-N’-methyl-stilbazoliumtosylate (DAST) at the wavelength of 520 nm are investigated by femtosecondopen-aperture Z-scan technique and transient absorption spectroscopy,respectively. Z-scan measurements indicate that DAST solution exhibitsultra-high nonlinear saturable absorption (SA) responses with a figure ofmerit of 4.57 × 10~(?1)3 esu cm and a saturation strength of 3.20 GW cm~(?2), farsuperior to those of the most known 2D SA materials under similar excitations.Transient absorption results reveal that the outstanding SA performancesof the solution-phase DAST are rooted in ultra-fast ground-statebleaching based on the Pauli blocking effect. The subsequent excited statecarrier relaxation processes are dominated by rapid intraband carrier coolingand defect-assisted interband Auger recombination. Moreover, high-qualityDAST?polyvinyl alcohol composite films prepared by solution casting exhibitsimilar ultra-high SA responses and reliable long-term stability without anydegradation of their SA responses even after exposure to air moisture for 100days. These findings establish an experimental and theoretical foundation forthe development of high-performance ultra-fast optoelectronic devices basedon organic NLO materials in the future.