With the extended π-electronic delocalization, organic 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) exhibits excellent third-order saturation absorption and optical limiting properties, but rare results about its third-order nonlinear emission have been previously reported. In this work, a flexible DAST−polyvinyl alcohol composite film was prepared, and its nonlinear emission properties were systematically characterized. Results reveal that besides a distinct second harmonic generation signal originating from the non-centrosymmetric macroscopic packing of the DAST chromophores, a strong third-order two-photon excited fluorescence signal was also measured from the composite, as experimentally confirmed by a quadratic dependence of the emission intensity on the pumped intensity. These nonlinear emission behaviors reveal that ionic organic DAST molecules hold great potential applications in laser frequency conversion and optical imaging.
Organic non-linear waveguides based on 4-N,N-Dimethylamino-4’-N’-methyl-stilbazolium tosylate (DAST) were directly grown by a cooling soft template method. Results revealed that as-yielded DAST hydrate waveguides (HWs) exhibit excellent waveguide performance, exciton polariton, and fluorescence properties, which can be rationally controlled by the annealing temperature. The red shift fluorescence excitation and emission spectra in the annealed DAST HWs are attributed to the recrystallization and J-aggregation of the chromophore cations in a head-to-tail stacking mode, which increase the charge transfer efficiency from one chromophore to another. Particularly, the fluorescence can propagate along the DAST HWs axis due to the produced exciton polaritons. Moreover, the annealed DAST HWs exhibit strong second harmonic generation (SHG) intensity, but no SHG activity was observed in DAST HWs. These findings further extend the applications of DAST HWs into a wide range of fields, such as integrated optical modulation, micro lasers, and fluorescent
Owing to their exceptional electrical, optical and mechanical properties, carbon nanotubes (CNTs) are highly attractive and widely applied in the fields of material, chemistry, physics, etc. Recently, CNT-based composites films have attracted more and more attention. In this work, composite films composed by patterned CNTs (PCNTs) and vanadium oxide (VOx) were prepared by combining two techniques of spin-coating and spray-coating. Results reveal that VOx– PCNT composite films with different CNT patterns, including stripe, square, and parallelogram CNT shapes, were successfully prepared. The as-prepared VOx–PCNT composite films exhibit different electrical and optical properties. Particularly, under the same CNT quantity, the VOx–PCNT composite films containing higher dispersion of CNTs exhibit lower resistance (R). A low R of 343 kΩ was measured at room temperature from the composite film with a stripe CNTs’ pattern and a high dispersion of 33.3%. Moreover, UV-vis measurements indicate that the order for the optical absorption of the composite films is: stripe < square < parallelogram, revealing the increase of the absorption with the increase of the CNTs’ dispersion. Furthermore, after CNTs’ addition, the infrared absorption similarly increases, while the optical band gap decreases. These suggest that both the electrical and optical properties of VOx films can be rationally adjusted by changing the deposited CNTs’ patterns. Thus, we describe a new route to the control of the optical and electrical properties of metal oxides by the CNTs’ pattern.
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