Synthesis And Applications Of Silica-based Luminescent Composites

Silica-based luminescent composites have many advantages,such as good biocompatibility,high chemical stability,and easy surface functionalization.They have great application prospects in biological imaging,chemical sensing,optoelectronic device,anti-counterfeiting technology.However,current luminescent silica-based composite materials have problems such as complex preparation process,low loading efficiency,poor photostability and low quantum yield.In this paper,based on the in-situ synthesis strategy,we prepared a series of silica-based composites with excellent luminescent properties and photostability,studied their luminescent mechanism,and explored their applications in cell imaging,anti-counterfeiting labels,fabrication of LEDs and detection.In chapter two,we synthesized a novel red-emitting organosilica nanoparticles(OSi NPs)with high quantum yield,high photostability,low toxicity and good biocompatibility by using 3-aminopropyltrimethoxysilane and indocyanine green.The experimental results show that the enhanced photostability of the synthesized OSi NPs is mainly due to the fast radiative transition rate of OSi NPs and thus the low yield of reactive oxygen species.This red luminescent material is a potential fluorescent probe for long-term biological imaging.In addition,this method also provides a new strategy for improving the photostability of fluorescent dyes.In chapter three,we synthesized a kind of core-shell structure of silane-modified carbon dots(Si CDs)using aminosilane and phytic acid as precursors.The maximum PLQY of Si CDs could achieve 56.3%.The core as the luminescence center,and the silica network as the protective layer that can prevent the aggregation of the luminescence center,so that the Si CDs will not undergo aggregation caused quenching in the solid-state.Due to the unique core-shell structure,the Si CDs have bright blue emission in both dispersion and solid-state,and have high thermal and photostability.In addition,Si CDs can be covalently coupled with the glass matrix,ensuring the preparation of composite glass has good transparency,controllable loading efficiency and efficient UV shielding performance.In chapter four,using tetramethylammonium hydroxide(TMAOH)as both the catalyst for preparing silica particles and the precursor for carbon dot,silica-coated nitrogen-doped carbon dots(N-CDs@SiO₂)were in-situ prepared by pyrolysis.The emission color of N-CDs@SiO₂ particles can be tuned from blue,green to yellow by changing the concentration of TMAOH in the reaction.Due to the protective effect of the silica matrix,N-CDs@SiO₂ exhibits bright and stable emission in both solution and solid,and can be used for the construction of anti-counterfeiting labels and light-emitting devices.In chapter five,we used 3-mercaptopropyltrimethoxysilane(MPTS)as the ligand to rapidly synthesize gold nanoclusters(MPTS-Au NCs)within 3 minutes.It was found that MPTS-Au NCs have the property of aggregation-induced emission enhancement,which can be used for the detection of zinc ions and protamine.Because the surface ligand of MPTS-Au NCs is organosilane,which can be co-hydrolyzed/condensed with TEOS in St(?)ber reaction to incorporate MPTS-Au NCs into silica matrix,the coating efficiency of MPTS-Au NCs can reach 100% and the stability is greatly improved.