Study On Preparation Of Carbon Dots And Their Application In Organic Light Emitting Diodes

Carbon dots(CDs)are new nano materials with size below 10 nm.They have low toxicity,strong stability,good biocompatibility,easy functionalization and many other advantages.Meanwhile they have efficient fluorescence.CDs are expected to be used in bioimaging,sensors,photocatalysis,light emitting diodes and so on.In short,CDs have broad application prospects.This thesis mainly studied the preparation method of CDs and their use in organic light emitting diodes.The main contents of the paper are as follows:(1)We prepared CDs with citric acid and urea as materials,by microwave method.Then we measured the absorption spectrum and the fluorescence spectroscopy.Through the results,we analyzed the fluorescence characteristic of CDs.After that,we proved that doping nitrogen can obviously enhance the fluorescence of CDs by changing the mass ratio of citric acid and urea.On the other hand,we changed the solvent of CDs and found that CDs have better fluorescence in ethanol solution than in aqueous solution.(2)In order to prevent solid-state luminescent quenching of CDs caused by aggregating,and better to be applied to solid light emitting devices,we prepared CDs-based phosphors with starch as carrier.We found that the fluorescence spectroscopy of CDs-based phosphors is almost identical to that of CDs in shape.This indicates that starch does not affect the fluorescence properties of CDs,and completely can be used as carrier of CDs to prepare phosphors.Next,we used glucose instead of starch to do a similar experiment,the results showed that glucose is also a suitable carrier of CDs.(3)Apply the CDs-based phosphors to blue light emission OLEDs,then we got cold white light emission OLEDs based on photoluminescence of CDs.(4)Use CDs as light emitting layer to prepare CDs electroluminescent diodes with the structure of ITO/m-MTDATA/NPB/CDs/Alq3/Al.The devices emitted yellow green light with a emission at 550 nm,and the color coordinates were(0.40,0.55).(5)Apply CDs to middle of the organic layers of OLEDs to prepare blue light emission OLED,yellow light emission OLED and white light emission OLED.It is found that carbon dots are not used as luminous materials in OLEDs,but as auxiliary materials to improve the hole injection efficiency in devices.CDs can improve the performance of OLEDs without changing the luminous nature of the device.We offered new ideas for manufacturing efficient OLED.The innovation of this paper is as follows:(1)Use ethanol instead of water as the solvent of CDs.The prepared CDs ethanol solution has a higher fluorescence intensity than that of CDs aqueous solution.(2)In this paper,we prepared quantum dot OLEDs by introducing CDs into OLED,and improved the luminous performance of OLEDs.