RESUMEN
Covalent organic frameworks (COFs) have gained considerable attention due to their highly conjugated π-skeletons, rendering them promising candidates for the design of light-emitting materials. In this study, we present two vinylene-linked COFs, namely, VL-COF-1 and VL-COF-2, which were synthesized through the Knoevenagel condensation of 2,4,6-trimethyl-1,3,5-triazine with terephthalaldehyde or 4,4'-biphenyldicarboxaldehyde. Both VL-COF-1 and VL-COF-2 exhibited excellent chemical and thermal stability. The presence of vinylene linkages between the constituent building blocks in these COFs resulted in broad excitation and emission properties. Remarkably, the designed VL-COFs demonstrated bright emission, fast fluorescence decay, and high stability, making them highly attractive for optoelectronic applications. To assess the potential of these VL-COFs in practical devices, we fabricated white-light-emitting diodes (WLEDs) coated with VL-COF-1 and VL-COF-2. Notably, the WLEDs coated with VL-COF-1 achieved high-quality white light emission, closely approximating standard white light. The promising performance of VL-COF-coated WLEDs suggests the feasibility of utilizing COF materials for stable and efficient lighting applications.
RESUMEN
Covalent-organic frameworks (COFs) are a new class of porous crystalline frameworks with high π-conjugation and periodical skeletons. The highly ordered π-conjugation structures in some COFs allow exciton migration and energy transfer over the frameworks, which leads to good fluorescence probing ability. In this work, two COFs (TFHPB-TAPB-COF and TFHPB-TTA-COF) are successfully condensed via the Schiff base condensation reaction. The intramolecular hydrogen bonds between imine bonds and hydroxyl groups form the excited-state intramolecular proton transfer (ESIPT) strategy. Owing to intramolecular hydrogen bonds in the skeleton, the two COFs show high crystallinity, remarkable stability, and excellent luminescence. The COFs represent a good sensitivity and selectivity to fluoride anions via fluorescence turn-off. Other halogen anions (chloride, bromide, and iodine) and acid anions (nitrate and hydrogen carbonate) remain inactive. These results imply that only fluoride anion is capable of opening the hydrogen bond interaction and hence break the ESIPT strategy. The detection limit toward fluoride anion is down to nanomoles level, ranking the best performances among fluoride anion sensors systems.
RESUMEN
A combinatorial method was employed to rapidly screen the effects of La, Ce-co-doping on the luminescent properties of Gd2Si2O7 pyrosilicate using an 8 × 8 library. The candidate formulations (Gd1-x-yLax)2Si2O7:Ce2y were evaluated by luminescence pictures under ultraviolet excitation. The optimal composition was found to be (Gd0.89La0.1)2Si2O7:Ce0.02 after scaled-up preparation and detailed characterization of powder samples, which shows an excellent light output under both ultraviolet and X-ray excitation (about 5.43 times of commercial YAG:Ce powders). The XRD results indicate that the phase structure sequence is tetragonal-orthorhombic-triclinic for different calcination temperatures and doping ions. The (Gd0.89La0.1)2Si2O7:Ce0.02 powder sample also demonstrated excellent temperature stability of luminescence up to 200 °C and a short decay time of several tens of nanoseconds, suggesting that this may represent a new kind of scintillation material, such as single crystals, ceramics, glass, or phosphors.
