In-situ Adjustment And Performance Of Solid-state Fluorescence And Phosphorescent Carbon Pots

Carbon dots(CDs)are nano-scale optoelectronic materials with excellent fluorescence or phosphorescence properties.Owing to their adjustable luminescence spectrum,good photobleaching resistance,and low toxicity,they are promising to be used in biological imaging,substance detection,lighting,and information security.At present,the emission spectrum of fluorescent CDs can be adjusted from blue to red,so the application of CD phosphors to white lightemitting diodes(LEDs)has broad prospects.However,there are not only hindered by the complicated preparation and purification processes,but also limited by low device manufacturing efficiency because of the employ of multi-color phosphors which used for high color rendering index(CRI)of white LEDs.As for phosphorescent CDs,in order to emit phosphorescence at room temperature,CDs are usually introduced special groups or embedded in solid substrates.The former requires complex treatment methods,high cost and exhibits high toxicity,while the latter is more commonly used for room temperature phosphorescence(RTP)CDs,but is realized in multi-step processes.In order to overcome the above deficiencies,this paper uses a one-step solvothermal method,filtering purification treatment,and the same reaction raw materials to achieve both the multi-emission peak solid-state fluorescent CDs and RTP CDs only by adjusting the reaction temperature.The main contents are as follows:(1)In-situ preparation of solid-state fluorescent CDs and their application on white LEDs.In order to avoid the aggregation of CDs,CDs embedded in phthalimide crystals were designed and synthesized by solvothermal method.Solid-state yellow fluorescent CDs(CDs/PC)were prepared by using phthalic acid and formamide as raw materials,and ethylene glycol and glycerol as solvents,separately.CDs/PC realized the uniform dispersion of CDs in phthalimide crystals,and because of macro size,CDs/PC were obtained by simple filtering and drying without any other purification steps.The fluorescence spectrum of CDs/PC covers the green,yellow,and orange regions of visible light.Therefore,a white lightemitting diode(LED)with a CRI of 82 and a correlated color temperature of 5430 K was prepared by combining CDs/PC with a blue LED chip.(2)In-situ preparation and properties of RTP CDs.The same preparation method and raw materials(solvent is ethylene glycol)for the above solid fluorescent CDs was used to prepare RTP-CDs,except that the reaction temperature was increased to 220 °C.RTP-CDs had a similar structure with above CDs/PC: polymer-like CDs were embedded in an organic crystal matrix.Owing to the construction of hydrogen bonds between CDs and the crystal matrix,the efficiency of intersystem crossing is improved,the groups on CDs are fixed,and the vibration dissipation is reduced,which benefits the phosphorescent properties at room temperature.The product was obtained without any further purification treatments,only by filtering and drying.The afterglow duration of RTP-CDs was about 2.7 s and the average phosphorescence lifetime was 0.47 s.