Photoactive nanomaterials exhibit myriad customized properties, including a photon converting ability, specific surface area, physicochemical stability, and chemical reactivity, making them appealing ...for a wide range of practical applications ....
A deep understanding of the photoluminescence (PL) from aggregated graphene quantum dots (GQDs) is very important for their practical applications. Here the PL spectra from GQDs solutions at ...different concentrations are studied. We find that the intensity of the green emission (ca. 530–560 nm) linearly relies on the concentration of GQDs, whereas the blue PL (ca. 425 nm) intensity is below the linear relationship, indicating a concentration-induced partial quenching of blue PL. Confocal fluorescence images explicitly demonstrate the aggregation of GQDs at high concentration. The concentration-induced PL quenching is successfully interpreted by a model of photon reabsorption and nonradiative energy transfer, indicating that, at the aggregated states, the excited electrons of GQDs may nonradiatively relax to ground states through couplings with neighboring ones. Simulated fluorescence decay results show that the energy transfer between neighboring GQDs results in a prolonged dwell time of electron on high-energy state and thus increases the decay time of 425 nm emission, while 550 nm emission remains unaffected, which is consistent with the experimental results. This work will contribute to a deep understanding on PL of GQDs and is also of huge importance to extend GQDs’ applications.
Photocatalysts possessing high efficiency in degrading aquatic organic pollutants are highly desirable. Although graphene-based nanocomposites exhibit excellent photocatalytic properties, the role of ...graphene has been largely underestimated. Herein, the photothermal effect of graphene-based nanocomposites is demonstrated to play an important role in the enhanced photocatalytic performance, which has not been considered previously. In our study on degradation of organic pollutants (methylene blue), the contribution of the photothermal effect caused by a nanocomposite consisting of P25 and reduced graphene oxide can be as high as ∼38% in addition to trapping and shuttling photogenerated electrons and increasing both light absorption and pollutant adsorptivity. The result reveals that the photothermal characteristic of graphene-based nanocomposite is vital to photocatalysis. It implies that designing graphene-based nanocomposites with the improved photothermal performance is a promising strategy to acquire highly efficient photocatalytic activity.
Photon recycling and carrier diffusion are the two plausible processes that primarily affect the carrier dynamics in halide perovskites, and therefore the evaluation of the performance of their ...photovoltaic and photonic devices. However, it is still challenging to isolate their individual contributions because both processes result in a similar emission redshift. Herein, it is confirmed that photon recycling is the dominant effect responsible for the observed redshifted emission. By applying one‐ and two‐photon confocal emission microscopy on Ruddlesden–Popper type 2D perovskites, of which interplane carrier diffusion is strictly suppressed, the substantial PL redshift (72 meV) is well reproduced by the photon transport model. A comparison of 3D bulk CH3NH3PbBr3 single crystal to 2D perovskite by depth‐resolved two‐photon PL spectra reveals the contribution of carrier diffusion on energy transport at a distance beyond diffusion length is constantly negligible, though the carrier diffusion indeed exists in the 3D crystal. The investigation resolves the fundamental confusion and debate surrounding the issue and provides significant insights into carrier kinetics in perovskites, which is important for future developments in solar cells and other optoelectronic devices.
Photon recycling and carrier diffusion are the two plausible processes that primarily affect the carrier dynamics in halide perovskites, and therefore the evaluation of the performance of their photovoltaic and photonic devices. However, it is still challenging to isolate their individual contributions. Herein, it is confirmed that photon recycling is the dominant effect responsible for the observed redshifted emission.
Spontaneous polarization reversal: Saturated polarization–electric field loops with a concave region were obtained from diphenylalanine peptide microtubes (FF PMTs) by combining the action of light ...during the hysteresis loop measurements (see picture; Ec=coercive field). The existence of ferroelectricity in FF peptide nanostructures was shown experimentally. The ferroelectricity of the FF PMTs is expected to extend their applications to biomedicine and microelectronics.
Using abundant solar energy to generate steam offers unique solution overcoming the lack of freshwater resources. Despite extensive explorations, low-cost devices with high efficiency are still ...critically wanting. In this work, the extremely cheap carbonized kelp with good stability, high solar absorption (∼93%), porous microstructure, and hydrophilic surface is found to be efficient for solar steam generation (SSG) and seawater desalination for the first time. A SSG device meeting the requirements of the “most stable triangle” is thus designed. The carbonized kelp is utilized as the solar absorber, with thermal insulation by an expanded polystyrene foam and water supply by a fiber cotton wick via the capillary force. A high solar to steam conversion efficiency of 84.8% and evaporation rate of 1.351 kg·m-2·h-1 are attained under 1 sun irradiation. This work develops a promising and bioinspired device with long-term stability for SSG that can be produced economically (∼3.8 $/m2).
2D organic–inorganic hybrid Ruddlesden–Popper perovskites (RPPs) have recently attracted increasing attention due to their excellent environmental stability, high degree of electronic tunability, and ...natural multiquantum‐well structures. Although there is a rapid development of photoelectronic applications in solar cells, photodetectors, light emitting diodes (LEDs), and lasers based on 2D RPPs, the state‐of‐the‐art performance is far inferior to that of the existing devices because of the limited understanding on fundamental physics, especially special photophysics in carrier dynamics, excitonic fine structures, excitonic quasiparticles, and spin‐related effect. Thus, there is still plenty of room to improve the performances of photoelectronic devices based on 2D RPPs by enhancing knowledge on fundamental photophysics. This review highlights the special photophysics of 2D RPPs that is fundamentally different from the conventional 3D congeners. It also provides the most recent progress, debates, challenges, prospects, and in‐depth understanding of photophysics in 2D perovskites, which is significant for not only boosting performance of solar cells, LEDs, photodetectors, but also future development of applications in lasers, spintronics, quantum information, and integrated photonic chips.
This review highlights the special photophysics of 2D perovskites that is fundamentally different from the conventional 3D congeners, which is significant for not only boosting performance of solar cells, light emitting diodes, photodetectors, but also future development of applications in lasers, spintronics, quantum information, and integrated photonic chips.
Carbon nitrides synthesized by thermal polycondensation of melamine at 700 ~C exhibit photoluminescence （PL） ranging from 400 to 650 nm. This broad PL is attributed to band to band transitions and ...bandtail transitions of lone pair （LP） states of intra-tri-s-triazine and inter-tri-s-triazine nitrogens. The proposed PL mechanism is further confirmed by diffusion reflectance spectroscopy, as well as time-resolved and temperature-dependent PL. This intense fluorescence is stable at different pH and resistant to UV exposure, suggesting that this inexpensive broadband luminescent material could be significant for white- light-emitting （WLE） applications. Thus, quasi-WLE films and membranes with designed patterns are fabricated by embedding the carbon nitrides into polymethyl methacrylate. Moreover, even broader PL （400 to 740 nm） is acquired in com- posite films composed of carbon nitrides, further suggesting that the carbon nitrides are robust candidates for WLE.
Despite intensive efforts, the fluorescence of perovskite nanocrystals (NCs) still suffers from a poor color purity, which limits the applications in light emitting and multicolor display. A deep ...understanding on the fundamental of the photoluminescent (PL) spectral broadening is thus of great significance. Herein, the PL decay curves of the CsPbCl
Br
NCs are monitored at different wavelengths covering the entire PL band. Moreover, energy relaxation time τ and radiative recombination time β are obtained by numerical fittings. The dependences of τ and 1/β on the detection wavelength agree well with the steady-state PL spectrum, indicating the observed PL broadening is an intrinsic effect due to the resonance and off-resonance exciton radiative recombination processes. This work not only provides a new analysis method for time-resolved PL spectra of perovskites, but also gains a deep insight into the spectral broadening of the lead halide perovskite NCs.
•Poly(ethylene glycol)/carbon quantum dots (PEG/CQDs) composite solid films exhibiting strong and tunable blue–red emission were prepared. Successful preparation of tunable emitting CQDs solid films ...can extend the application of carbon quantum dots in photoelectric devices.•The mechanism of the tunable emission from the PEG/CQDs composite solid films was discussed.•On the basis of the characteristics of the PL from solid films in this work, the complex PL origins of CQDs were further defined. The PL mechanism provides insights into the fluorescence mechanism of CQDs and may promotes their applications.•Poly(ethylene glycol); carbon quantum dots; Strong and tunable blue-red emission; The fluorescent quantum yield of 12.6%.
Although carbon quantum dots (CQDs) possess excellent luminescence properties, it is a challenge to apply water-soluble CQDs to tunable luminescent devices. Herein, quaternary CQDs are incorporated into poly(ethylene glycol) to produce poly(ethylene glycol)/CQD composite solid films which exhibit strong and tunable blue–red emission. The fluorescent quantum yield reaches 12.6% which is comparable to that of many liquid CQDs and the photoluminescence characteristics are determined to elucidate the fluorescence mechanism. The CQD solid films with tunable optical properties bode well for photoelectric devices especially displays.
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