| Red carbon dots(CDs)have advantages of deep penetration and low radiation damage,and red emission is also necessary primary color to achieve white light emitting diodes(LEDs).However,red CDs still suffer from complex synthetic schemes,controversial mechanism and lower quantum efficiency(QY).In this thesis,a series of long-wavelength CDs were synthesized by hydrothermal method,and the luminescence mechanism of CDs was investigated by tailoring surface states of CDs with amino groups.Morover,the IIIA group elements(B,Al,Ga)doping and Au nanoparticles were used to improve the QY of red CDs.In addition,the obtained CDs are applied to the fields of white LEDs and anti-counterfeiting.Firstly,a series of CDs with long-wavelength emission were synthesized using different synthetic schemes,including p-CDs(?em=605 nm),CA-CDs(?em=590 nm),Da-CDs(?em=599 nm),Trp-CDs(?em=587 nm),Urea-CDs(?em=591 nm),RCDs(?em=595nm,665 nm),and the emission wavelength covers the range from orange to deep red.The synthesis temperature of RCDs within 120-140°C is the lowest temperature in reported references,and the red light emission of RCDs was mainly related to C=O related bonds.Secondly,the surface states of p-CDs were modulated by amino groups.The effects of different N structures on surface state emission for CDs were investigated.It is found that the multiple emission states are related to the speciation of nitrogen(pyridinic N,pyrrolic N,graphitic N and amino N)on the surface of CDs,in which fluorophore formed by the deformation of p-phenylenediamine contributes to the red emission,pyridinic N is responsible for green emission state,and pyrrolic N can enhance the blue emission.In addition,the modulated CDs with multiple emission states can be used as single light converter to fabricate a white LED,which has white light color coordinate of(0.31,0.32),high color rendering index(CRI)of 85,luminous efficiency of 8.8 lm/W and good stability.Finally,group IIIA(B,Al,Ga)elements were firstly selected to improve the QY of RCDs by doping and the QY can be significantly increased from 0.29%to 12.02%,1.99%and 1.53%for B-CDs,Al-CDs and Ga-CDs,respectively.The improvement of QY for RCDs is based on same mechanism.On the one hand,IIIA elements doping can increase the crystallinity through changing the configurations of the C and N bonding status.On the other hand,the formation of C-N-IIIA-O bonds via doping can suppress the non-radiative transition due to electron-withdrawing effects,thus improving the QY of RCDs.Furthermore,B-CDs with high QY and acid-induced discoloration are successfully applied to white LED and a new anti-counterfeiting technology with double measures,respectively.In addition,the localized surface plasmon resonance(LSPR)effects of Au NPs were also used to enhance the luminescence intensity of p-CDs by 2.3 times,and the enhancement mechanism was originated from excitation enhancement. |
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