Controllable Preparation Of Color-changing Room Temperature Phosphorescent Carbon Dots And Its Anti-counterfeiting Application

As a new luminescent carbon nano-material,carbon dots(CDs)have attracted wide attention because of its simple preparation,low cost,good photostability and low toxicity,and have been widely used in biology,optoelectronics and energy-related fields.Up to now,many literatures have reported examples of fluorescent carbon dots,but the synthesis and optical properties of room temperature phosphorescent carbon dots are rarely reported because excitons excited singlet are difficult to transition to excited triplet and are easily inactivated by vibration and quenched by oxygen at room temperature,which makes phosphorescence more difficult than fluorescence.Moreover,at present,Reported room temperature phosphorescent carbon dots are limited to metalcontaining inorganic substances and organometallic complexes,and the existence of heavy metals in these materials inevitably leads to high toxicity,high cost,limited resources and complicated preparation process.Therefore,it is still an arduous challenge to realize full-color adjustable phosphorescent carbon dots and multi-mode adjustable dynamic color-changing phosphorescent carbon dots in a single system.In this thesis,a series of room temperature phosphorescent carbon dots with excellent optical properties were successfully synthesized and applied to information encryption and anti-counterfeiting.The morphological characteristics were observed by highresolution transmission electron microscope,and the elemental composition and functional groups of the synthesized room-temperature phosphorescent carbon dots were analyzed by FTIR,XPS and NMR,so as to further explore the luminescence mechanism of the room-temperature phosphorescent carbon dots.The main research work of this thesis is as follows:(1)Using ethylenediamine tetraacetic acid,phosphoric acid and boric acid as raw materials,room temperature color-changing phosphorescent carbon dots were synthesized by one-step method under heating conditions.The carbon dots of synthesized room temperature phosphorescence are uniformly dispersed,and the color of room temperature phosphorescence changes from yellow to green with naked eyes.The quantum yield of phosphorescence is as high as 21.73%,the lifetime of triplet phosphorescence is 180 ms,and the afterglow time is as long as 7 s.By comparing the room temperature phosphorescent carbon dots prepared under different reaction conditions,the optical characteristics,morphology and related structural properties of room temperature photochromic phosphorescent carbon dots are analyzed,and the luminescence mechanism is further analyzed.Finally,the color-changing room temperature phosphorescent carbon dots are applied to pattern anti-counterfeiting and fingerprint anti-counterfeiting.(2)Using hydroxyurea and terephthalic acid as raw materials,adopting a solventfree method of environmental protection,and adjusting the adding ratio of hydroxyurea and terephthalic acid,we synthesized blue,green and Huang San phosphorescent carbon dots without substrate at room temperature in one step,realizing the adjustable room temperature phosphorescence color in the long wavelength range(435nm-595nm).In addition,1,8-naphthalimide and boronic acid were chosen as raw materials for the synthesis of red room-temperature phosphorescent carbon dots by a solvent-free method.The phosphorescence lifetimes of blue,green,yellow and red carbon dots are1837.38,1406.75,1530.12 and 1320.30 ms respectively,and the afterglow time under naked eye observation is as long as 10 s,7 s,8 s and 6 s respectively.Then,the optical characteristics,morphology and related structural properties of four kinds of multicolor room temperature color-changing phosphorescent carbon dots were analyzed by preparing comparative samples at maximum and minimum temperatures,so as to further analyze the luminescence mechanism.In this thesis,the multi-color afterglow characteristics of these four carbon dots are applied to multi-coding encryption and pattern anti-counterfeiting.