Preparation Of Phosphazene Carbon Dots And Their Room Temperature Phosphorescence Properties

Long-life room temperature phosphorescent materials(RTP)are important luminescent materials,which have wide applications in detection,anti-counterfeiting,information protection and so on due to the spin suppression property of triple exciton transition.When a material in its ground state is irradiated by excited light,electrons in the molecule absorb the energy of the photons and jump back into an excited state.Excited electrons decay back to the ground state either by means of a non-radioactive jump or by means of a radiation jump.Non-radiative transitions will lose energy in the form of heat or other forms,while radiative transitions will generate luminescence behavior in the form of photons.Fluorescence and phosphorescence are photoluminescence.Long-lived room temperature phosphorescence materials(RTP)emit phosphorescence time can reach the millisecond level,so far,many RTP preparation is still limited to organic-metal complexes and pure organic synthesis,synthesis process is complex,toxic,high cost.As a new type of photoluminescent nanomaterials,carbon dot(CD_S)has been regarded as a good room temperature phosphorescent material with long life due to its wide selection of raw materials,various synthesis methods,low production cost and excellent photostability.CDs can be synthesized from a wide variety of raw materials as long as it is organic.Such as small molecules of organic matter,large molecules of natural organic matter.Many organic matter in daily life can also be directly used as raw materials of carbon point,such as vegetables,fruits,and even various wastes.Carbon dot synthesis methods are also various,summed up into two main categories,one is the"top-down method",the other is the"bottom-up method".The"top-down method",as the name suggests,is to strip smaller CD_S from larger carbon structures,such as activated carbon,graphene and carbon nanotubes,etc.The synthesis methods are often more complex,the reaction time is long,and the reaction conditions are relatively high.On the contrary,the"bottom-up method"refers to the synthesis of CD_S with small molecules containing carbon through microwave,ultrasound,carbonization and other methods.Microwave,ultrasound,carbonization and other methods are relatively simple,and not strict in conditions.The choice of carbon source is always the most important and primary problem in the research.In previous studies,organic chemical reagents are mostly used as carbon sources,which are harmful to environment and human body.In this study,natural green chitosan was used as carbon source to obtain long life room temperature phosphorescent carbon dots(CD_S)by microwave-assisted heating of chitosan and phosphoric acid aqueous solution.Through a series of characterization(XPS,UV-Vis,FT-IR,TEM,etc.),it is found that the successful doping of P element makes the phosphorescence properties of this kind of carbon quantum dot materials reach the visual(second level)effect.Chitosan was selected again,and phytic acid,which is abundant in plants,was selected as the phosphorus source for doping.The method of microwave-assisted heating of chitosan and phytic acid aqueous solution was used to obtain long-life room temperature phosphorescence carbon dots(Ph-CD_S).Through a series of characterization(XPS,UV-Vis,FT-IR and TEM,etc.),it is found that the successful doping of P element makes the phosphorescent properties of Ph-CD_S materials reach the visual(second level)effect,which indicates that this kind of luminescent materials have potential application value in the field of luminescence.