Synthesis Of High-eficiency Fluorescent Carbon Dots And Application In White Leds

Carbon dots?CDs?,as a new type of zero-dimensional carbon-based material,has been a dazzling star in new fluorescent materials in the research of just ten years since it was discovered in 2004.In terms of synthesis,CDs have the characteristics of abundant raw materials,simple and diverse preparation methods and low cost.In terms of performance,CDs have excellent luminous properties,are easy to modify,and have low toxicity and good biocompatibility.Besides,CDs are non-toxic and harmless to the environment.These outstanding advantages have enabled CDs to have certain applications in the fields of biological imaging,tumor treatment,analytical detection,photocatalysis and lighting.In recent years,the continuous improvement of the emission performance of CDs has made people pay more attention to the development of green lighting systems based on CDs for the production of white LEDs.At present,CD-based white LEDs mainly have the following problems:first,the fluorescent quantum yield?PL QY?of CDs is still generally low,which hinders the preparation of high-efficiency CD-based white LEDs;second,CDs usually suffer from aggregation-induced fluorescent quenching,which makes it difficult for CDs to obtain high PL QY in the solid state,and this restricts the practical application of CDs.Third,as an integral part of generating white light,CDs that emit yellow and red light are still difficult to prepare and the PL QY is very low.In view of these specific issues,this article will carry out in-depth research from three aspects:1.the synthesis of high-efficiency CDs;2.the realization of high-efficiency solid-state fluorescence of CDs;3.the preparation of high-quality CD-based white LEDs.The specific work is as follows:1.Synthesis of high-efficiency CDs.Using methyl red and o-phenylenediamine as precursors,yellow-emitting CDs?YCDs?with a PL QY of 95%were prepared by a solvothermal method,which is the highest value among the YCDs reported.The luminescence of YCDs mainly comes from the direct recombination of excitons.Due to the weak electro-acoustic coupling inside the CDs,the non-radiative recombination of carriers is suppressed,so the YCDs exhibit ultra-high PL QY.Through experimental and theoretical calculations,the relationship between the doped pyrrolic nitrogen in CDs and the Stokes shift of CDs is clarified.2.High-efficiency solid-state fluorescence of CDs were achieved.First,the fluorescence quenching of YCDs was successfully suppressed by embedding the YCDs in polystyrene.The PL QY of the composite film could reach 84%.Further,green-emitting CD powders?CDPs?with a PL QY of 75.9%were prepared by a one-step microwave method using citric acid,urea,and Na OH as raw materials.The CDs can be embedded in situ in the lattice structure of Na OH,thereby effectively suppressing aggregation-induced fluorescence quenching and obtaining fluorescence in solid state.3.Preparation of high-quality CD-based white LEDs.First,by combining the YCDs@PS composite film with a blue LED,a white LED was prepared,whose color coordinates are located at?0.32,0.34?,and the lumen efficiency is as high as 140lm/W,which is the highest value of the CD-based white LEDs.Then,based on the YCDs@PS composite film,a surface light source with an effective light emitting area of 100 cm^-2 was prepared,which further widened the application of CDs in the field of lighting.Finally,a white LED with a color rendering index of 93.5 was prepared by combining the CDPs with the red rare earth phosphor.In addition,the white LED has excellent spectral stability.We believe that this work will promote the research of the application of CDs in white LEDs,and have certain guiding significance for building high-efficiency green lighting systems based on CDs.