Preparation Of Carbon Dots And Their Fluorescence And Phosphorescence Properties

Fluorescent carbon dots(CDs)are found in recent years as a class of new carbon skeleton structure nanomaterial that have attracted immense attention because of their unique optical and low-toxic features.Although CDs have great application prospects in various aspects,their properties still need to be improved.Furthermore,the light absorption band of CDs are mainly limited to the blue and green(short-wavelength)region.The researches contained in this thesis are outlined as follows:(1)A unique dual-emissive S and N co-doped Carbon dots(S,N-CDs)were synthesized via one-pot hydrothermal method.The S,N-CDs not merely possess relatively high fluorescent quantum yield(QY)(43%),but also possess unique optical properties with dual-emission(blue and yellow)and excitation-independent properties.It is extremely rare for bare CDs have dual-emission properties under single excitation wavelength.We have done some comparative experiments to prove the unique properties of S,N-CDs are attributed to the co-doping effect of S and N atoms.The yellow emission comes from the intrinsic state emission and the blue emission comes from the CDs surface energy traps emission.We have achieved a series of solid-state lighting materials by using S,N-CDs as doping fluophor,such as silica encapsulated CDs(silica/S,N-CDs),light conversion film(LCF)and white-light-emitting diodes(WLED).This study presents a facile preparation of high-efficient dual-emission S,N-CDs and provides a new strategy to develop various solid-state fluorescent materials.(2)We have devised a universal and effective approach to awake the fascinating RTP of CDs by incorporating CDs into boric acid(BA)to form a glassy state(CDs/BA).This method not only have universal,but also allows CDs exhibit stronger RTP than in other matrix.Even the RTP of heteroatom-free CDs are incrediblely exhibited.Heteroatom-free CDs occupy fewer energy level structures that can undergo electron transitions and therefore are more difficult to possess RTP.Through the method a new B-O bond between CDs and BA can perfectly constitute a new electronic transition energy level that exactly reduces the energy gap between the singlet and triplet states,thereby effectively increasing the quantity of triple excitons.Meanwhile the glassy state can effectively protect the excited triplet of CDs/BA from the energy loss caused by rotation or vibration process,thus honest protecting the triple excitons.Through this one-step heat treatment method,we have obtained a series of outstanding metal-free RTP materials: the higest phosphorescence quantum yields(17.5%)and the longest phosphorescence lifetime(2.2s)CDs-based RTP materials,and charming orange RTP materials.Ours results also exhibit that the persistent metal-free RTP materials have great potential in anti-counterfeit technology and information encryption.This approach introduces a new perspective to exploit the permanent RTP of metal-free materials.