Preparation And Solid-state Luminescence Of Carbon Dots And Relevant Composites

Carbon dots?CDs?, a promising zero-dimensional carbon nanomaterial, have been developed for bioimaging,security, photocatalysis, sensors and photoelectronicdevices. So far most of the studies have focused on the fluorescence of CDs in aqueous surrounding, but there is only little work about the solid-state fluorescence from CDs hybridized with solid matrices, not to mention the one in aggregation state. The status of insufficient researches and information may retard the further development of CDs. In this work, therefore, we concentrate on preparing the CDs for solid-state fluorescence in either hybrid system or aggregation state, and investigating the relevant mechanism for laying foundation for CDs applying in emerging fields. The researches contained in this thesis are outlined as follows:?1? A unique dual-emitting core-shell carbon dot-silica-phosphor?CDSP? was constructed from carbondots?CDs?, tetraethoxysilane and Sr₂Si₅N₈:Eu²⁺ phosphor through a one-pot sol-gel method.Blue emitting CDs uniformly disperse in the silica layer covering the orange emitting phosphor via apolymerization process, which makes CDSP achieve even white light emission. Tunable photoluminescence of CDSP is observed and the preferable white light emission is achieved through changingthe excitation wavelength or controlling the mass ratio of the phosphor. When CDSP powders with aphosphor rate of 3.9% and 5.1% are excited at a wavelength of 400 nm, preferable white light emission isobserved, with Commission Internationale de l?Eclairage?CIE? coordinates of?0.32, 0.32? and?0.34, 0.32?,respectively. Furthermore, CDSP can mix well with epoxy resin to emit strong and even white light, andbased on this, a CDSP-based white LED with a high colour rendering index about 94 was fabricated.?2? Self-quenching of carbon dots in aggregation state is still difficult to be conquered bystructure design, and has limited the broad applications of this material. Here we report the nitrogen-doped carbon dots?NCDs? which exhibit yellow-green solid-statefluorescence in aggregation state as well as blue fluorescence in water or solidmatrices, and first discuss the mechanism of self-quenching-resistance and the red-shift between fluorescence of aggregation state and that of dispersion state. Furthermore,we have also constructed a unique dual fluorescent-morphology by justemploying one luminescent species, i.e., the self-quenching-resistant NCD powder, to realize white light-emission, and then succeeded in fabricating a white LED. Thisnovel concept may simplify the process and reduce the cost compared to existingmethods. Moreover, NCD-based white light-emitting film and spongy aerogel havebeen presented in this work as well, demonstrating the flexibility of processing and changing the forms thatmake carbon dots meet the requirements of special applications and open up new application directions.?3? It is found that PVA-chains give much advantage to the moisture-resistance of NCD powder that makes this luminescent species stand rigidly under ambient condition. And this PVA-rich structure also acts as tight barrier that effectively prevents oxygen from permeating the aggregates and quenching the triplet. Benefiting from these unusual features, the NCDs can exhibit observable solid-matrix room temperature phosphorescence, which has never been reported in other hydrophilic CDs or similar photoluminescent carbon nanomaterials so far.Such RTP of NCD aggregates may inspire CD-like materials to be applied in emerging field.Furthermore, the potential of application in temperature sensing was evaluated, which reveals that phosphorescence as well as fluorescence of NCD powder can be employed to estimate the temperature of samples.