Summary
It is still a challenge to design and synthesize novel switchable optical materials with ultrafast nonlinear optical (NLO) response in a broad spectral range. These materials have exhibited great application potential in many high-technology fields such as biological imaging, chemical sensors, optical data storage, laser protection, and controllable intelligent and optoelectronic devices. By using porphyrins with highly delocalized 18 π-electron conjugated system as functional building blocks, the first ether-linked porphyrin covalent organic framework materials (COF-Pors) with highly ordered lattice structure have been successfully synthesized. In contrast to the starting porphyrins that only exhibit reverse saturable absorption (RSA) response at 532 nm, the as-prepared COF-Pors shows large NLO effect in a broad range from visible to near infrared. Upon laser illumination, COF-Pors exhibits typical saturable absorption (SA) effect at lower incident laser energy, and RSA response at higher pulse energy.
High-quality crystalline nanostructured ZnO thin films were grown on sapphire substrates by reactive sputtering. As-grown and post-annealed films (in air) with various grain sizes (2 to 29 nm) were investigated by scanning electron microscopy, X-ray diffraction, and Raman scattering. The electron–phonon coupling (EPC) strength, deduced from the ratio of the second- to the first-order Raman scattering intensity, diminished by reducing the ZnO grain size, which mainly relates to the Fröhlich interactions. Our finding suggests that in the spatially quantum-confined system the low polar nature leads to weak EPC. The outcome of this study is important for the development of nanoscale high-performance optoelectronic devices.
The as‐prepared BPDQs:Y6:PVP blends, in which Y6 acts as nonfullerene acceptor, black phosphorus quantum dots (BPQDs) serve as donor, and polyvinylpyrrolidone (PVP) as a polymer matrix, can respond to both the electrical and optical stimuli. Using these blends as the active layer, the first bulk heterojunction device with the functions of organic photovoltaics and information storage, Al/BPQDs:Y6:PVP/indium tin oxide, is fabricated. When the applied voltages vary from 0 to −0.8 V, this device exhibits both the photoinduced resistive state changes and volatile photoresponse characteristic in the broadband visible region. The light illumination gives rise to the significantly decrease of the device resistance. Furthermore, it is also found that, when the applied voltages are changed from 0 to ± 3 V, this device shows a typical nonvolatile rewritable memory performance in the dark, with an ON/OFF current ratio of 8 × 103, a switching‐on voltage of −1.68 V, and a smaller switching bias window. Upon illumination with different wavelength light, both the switching‐on voltage and the ON/OFF current ratio of the device are found to be greatly decreased. This work can be expected to open a way to the integration of information storage, modulating and demodulating functions, photovoltaic effect, and photoelectric detection in an optoelectronic device.
To comprehensively understand the behaviors of the near-band-edge emission and green emission (NBE, GE), the volume-weighting (VW) model is adapted to take into account a dead layer of confined excitons.
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