RESUMEN
Food contamination and spoilage is a worldwide concern considering its adverse effect on public health and food security. Real time monitoring food quality can reduce the risk of foodborne disease to consumers. Particularly, the emergence of multi-emitter luminescent metal-organic frameworks (LMOFs) as ratiometric sensory materials has provided the possibility for food quality and safety detection with high sensitivity and selectivity taking advantage of specific host-guest interactions, pre-concentrating and molecule-sieving effects of MOFs. Furthermore, the excellent sensing performance of multi-emitter MOF-based ratiometric sensors including self-calibration, multi-dimensional recognition and visual signal readout is able to meet the increasing rigor requirement of food safety evaluation. Multi-emitter MOF-based ratiometric sensors have become the focus of food safety detection. This review focuses on design strategies for different multiple emission sources assembly to construct multi-emitter MOFs materials based on at least two emitting centers. The design strategies for creating multi-emitter MOFs can be mainly classified into three categories: (1) multiple emission building blocks assembly in a single MOF phase; (2) single non-luminescent MOF or LMOF phase as a matrix for chromophore guest(s); (3) heterostructured hybrids of LMOF with other luminescent materials. In addition, the sensing signal output modes of multi-emitter MOF-based ratiometric sensors have critically discussed. Next, we highlight the recent progress for the development of multi-emitter MOF as ratiometric sensors in food contamination and spoilage detection. Their future improvement and advancing direction potential for their practical application is finally discussed.
RESUMEN
Widely tunable color emission from a single pixel is a promising but challenging technology for quantum-dot light-emitting diodes (QD-LEDs). Even a QD-LED pixel with stacked multi-QD layers having different colors is likely to emit a monotonic color because the exciton recombination mostly occurs in 1 or 1.5 QD layers with better charge balance. In this study, an all-solution-processed QD-LED with electrically tunable color emission over a wide color range by introducing a charge modulation layer (CML) is developed. Specifically, the CML acted as a high and narrow energy barrier for electrons between two QD layers, and the electron drift is sensitively controlled via the field-dependent tunneling effect. Therefore, the charge distribution and balance in the two QD layers re-electrically tunable, which enhanced the color tunability. The color tuning range and quantum efficiency are effectively controlled depending on the CML material and thickness. In addition, the color change caused by the solvent effect in a QD-LED with dual QD layers is thoroughly investigated. The proposed method may advance the understanding of QD emission behavior with the use of CML and provide a practical approach for the actual application of color-tunable pixel technology.
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Recent climate modeling studies have concluded that cumulative carbon emissions determine temperature increase, regardless of emission pathways. Accordingly, the optimal emission pathway can be determined from a socioeconomic standpoint. To access the path dependence of socioeconomic impacts for cumulative carbon emissions, we used a computable general equilibrium model to analyze impacts on major socioeconomic indicators on a global scale for 30-50 pathways with different emission reduction starting years, different subsequent emission pathways, and three different cumulative 2100 emission scenarios (emissions that meet the 2 °C target, the 2 °C target emissions plus 10 %, and emissions producing radiative forcing of 4.5 W/m2). The results show that even with identical cumulative emission figures, the resulting socioeconomic impacts vary by the pathway realized. For the United Nations 2 °C target, for example, (a) the 95 % confidence interval of cumulative global gross domestic product (GDP) is 1355-1363 trillion US dollars (2010-2100, discount rate = 5 %), (b) the cumulative GDP of pathways with later emission reduction starting years grows weaker (5 % significance level), and (c) emissions in 2100 have a moderate negative correlation with cumulative GDP. These results suggest that GDP loss is minimized with pathways with earlier emission reduction followed by more moderate reduction rates to achieve lower emission levels. Consequently, we suggest an early emission peak to meet the stringent target. In our model setting, it is desirable for emissions to peak by 2020 to reduce mitigation cost and by 2030 at the latest to meet the 2 °C target.
RESUMEN
The intriguing and rich photophysical properties of three curved nanographenes (CNG 6, 7, and 8) are investigated by time-resolved and temperature-dependent photoluminescence (PL) spectroscopy. CNG 7 and 8 exhibit dual fluorescence, as well as dual phosphorescence at low temperature in the main PL bands. In addition, hot bands are detected in fluorescence as well as phosphorescence, and, in the narrow temperature range of 100-140 K, thermally activated delayed fluorescence (TADF) with lifetimes on the millisecond time-scale is observed. These findings are rationalized by quantum-chemical simulations, which predict a single minimum of the S1 potential of CNG 6, but two S1 minima for CNG 7 and CNG 8, with considerable geometric reorganization between them, in agreement with the experimental findings. Additionally, a higher-lying S2 minimum close to S1 is optimized for the three CNG, from where emission is also possible due to thermal activation and, hence, non-Kasha behavior. The presence of higher-lying dark triplet states close to the S1 minima provides mechanistic evidence for the TADF phenomena observed. Non-radiative decay of the T1 state appears to be thermally activated with activation energies of roughly 100 meV and leads to disappearance of phosphorescence and TADF at T > 140 K.
RESUMEN
Carbon Dots (CDs) are fluorescent carbon-based nanoparticles that have attracted increasing attention in recent years as environment-friendly and cost-effective fluorophores. An application that can benefit from CDs in a relatively short-term perspective is the fabrication of color-converting materials in phosphor-converted white LEDs (WLEDs). In this work we present a one-pot solvothermal synthesis of polymer-passivated CDs that show a dual emission band (in the green and in the red regions) upon blue light excitation. A purposely designed numerical approach enables evaluating how the spectroscopic properties of such CDs can be profitable for application in WLEDs emulating daylight characteristics. Subsequently, we fabricate nanocomposite coatings based on the dual color-emitting CDs via solution-based strategies, and we compare their color-converting properties with those of the simulated ones to finally accomplish white light emission. The combined numerical and experimental approach can find a general use to reduce the number of experimental trial-and-error steps required for optimization of CD optical properties for lighting application.
RESUMEN
Carbon-dot (C-dot) liposome consisting of several thousands of C-dots shows interesting photoswitching properties. The water-dispersible C-dot liposome possesses intrinsic photoluminescence (PL) and is stable against salt and photoirradiation. The PL of C-dot liposome can be turned off and then on under photoirradiation over the wavelength regions of 510-540 nm and 365-420 nm, respectively. Like reported C-dots, the C-dot liposome emits various colors when excited at different wavelengths. Having great stability and high contrast, images of individual C-dot liposome have been recorded, showing negligible photoblinking. Through a simple photolithographic approach, micropatterns of C-dot liposomes emitting different colors have been fabricated.
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Though the investigation on controlling the fluorescence properties of nanocrystals (NCs) with single emission has been widely reported, few efforts were spent on adjusting the fluorescence properties of NCs with multiple emission peaks. In this work, we successfully synthesized multicolor MnSe:ZnSe NCs with multiple emission peaks and developed a simple and accurate method to realize photoluminescence (PL) spectra (or color) adjustment. The PL of MnSe:ZnSe NCs has two distinct emission peaks, the trap emission of ZnSe at 475nm and Mn(2+)-induced emission at 585nm. By adjusting the nucleation temperature, the emission color of the NCs can be encoded according to the ratio of the emission intensities at 475 and 585nm. With the nucleation temperature rising from 0 to 70°C, the PL ratio between trap emission and Mn(2+)-induced emission can be consecutively changed from (1, 3) to (1, 0.5). In addition, the trap state is deeply inside the NCs rather than on NCs surface so that the trap emission is stable during environment change. Thus, these MnSe:ZnSe NCs hold great promise as novel single-particle coding labels for biomedical imaging.