One-step Synthesis Of Graphitic Carbon Nitride Based Green Fluorescent Material And Its Application

Graphitic carbon nitride,a polymeric semiconductor,possesses excellent physicochemical stability,unique electronic structure and suitable band gap,making it show potential applications in various fields such as photocatalysis.Recently,g-C₃N₄-based luminescent materials attract an increasing interest owing to its good fluorescent property with tunable emission.Up to now,g-C₃N₄ solid phosphors and suspensions containing quantum dots or nanosheets have been developed,which exhibited blue intrinsic emission or emitted green light due to the modification of function groups.However,it is found that the quantum yields of blue phosphors are lower than those of green ones.In this thesis,a g-C₃N₄-based green phosphor with high photoluminescent quantum yield?PLQY?was developed,and its applications into white light-emitting diodes?WLEDs?was explored.In this paper a g-C₃N₄-based green phosphor was presented,which just involved thermal polymerization of single precursor,2,4-diamino-6-phenyl-1,3,5-triazine,under the atmosphere of argon,to prepare phenyl-modified g-C₃N₄.The effects of the calcining temperature and time on the crystalline structure,chemical composition,morphology,optical absorption property,and PL emission behavior of the obtained samples were investigated systematically.It is found that the phenyl-modified g-C₃N₄ prepared at 400°C possesses the typical heptazine rings and emitted green light centered at 520 nm under the excitation of 365 nm;While,the PL intensity and QY decreases with the increasing calcining temperatures.Moreover,it is found that the sample prepared at 400°C for 20 min consisted of the unreacted precursor,and the phenyl-modified g-C₃N₄ prepared at 400°C for 40 min exhibits a strong green emission with a quantum yield of as high as 38.08%.And with the further increase in calcining duration,a reduction in PL emission intensity and PLQY occurred.Consequently,the g-C₃N₄-based green phosphor with high PLQY can be prepared by annealing 2,4-diamino-6-phenyl-1,3,5-triazine at 400°C for 40 min.Gaussian fitting revealed that the PL emission of the g-C₃N₄-based green phosphor consisted of four peaks centered at around 465,490,520 and 545 nm;and the green emission is attributed to the enhancement in the two peaks centered at 520 and 545 nm,originating from the change in the PI orbital energy level of PhCN.The application of the PhCN green phosphor into white light-emitting diodes?WLEDs?has been explored.PhCN was mixed with a blue phosphor,acid-treated g-C₃N₄?ACN?,and a red phosphor,2,7-bis?4-?tert-butylthio?phenyl?fluorenone?2DPAFO?,to obtain a kind of white phosphor.And the white phosphor was employed to fabricate WLEDs by combining a UV chip of 365-370 nm.The optimal mass fractions of the three phosphors has been obtained to be 93.46%for the blue phosphor,5.61%for the green one and 0.93%for the red one,at which the obtained WLED exhibited a Ra of 85.7 and a Tc of 3809 K.Simple preparation process along with high quantum yield make this phenyl-modified g-C₃N₄ green phosphor show potentials in practical applications.