Investigation On The Functionalization Of Boron Nitride Nanodots And Their Fluorescence And Phosphorescence Properties

In recent years,quantum dot materials have become a bright star in the display technology due to their excellent fluorescence properties.Boron nitride nanodots(BNNDs)materials also became a "hot-spot" due to their low toxicity,low cost,biocompatibility,thermal and chemical stability etc.Although the preparation methods,precursor materials and application of BNNDs have made remarkable progress,the fluorescence of BNNDs reported so far is mainly focused on blue wavelength band due to the wide bandgap of BN,which severely limits their applications.Secondly,less attention is paid on the phosphorescence performance of BNNDs due to the poor spinorbit coupling effect resulted from the wide bandgap.Based on the above analysis,this dissertation focuses on the effects of the compositions and surface states of BNNDs on their fluorescence and phosphorescence properties.The main results include:(1)Nitro functionalized BNNDs were prepared by etching method with synergistic effect of sulfuric acid and nitric acid.And the BNNDs emit green fluorescence.The precursor prepared by calcination method was stripped into boron nitride nanosheets in the ultrasonication process,and sulfuric acid can etch the defects induced by the doping of carbon and oxygen atoms on the nanosheets,resulting in the formation of BNNDs.At the same time,nitro functional groups were introduced to the surface of BNNDs by nitric acid,resulting in the red shift of fluorescence emission wavelength from 450 nm to 520 nm.The nitro functionalized BNNDs with green fluorescence can be applyed in fiber dyes.(2)PPD functionalized BNNDs(p-BNNDs)were prepared by dispersing blue fluorescent BNNDs with PPD in water and stirred.The BNNDs with blue fluorescence were prepared by liquid phase sintering method,which contained abundant hydroxyl,amino and other functional groups on the surface.These functional groups can provide reaction sites for further functionalization of PPD molecules.As a result,the fluorescence of BNNDs shifted from 460 nm to 510 nm.Further studies revealed that the hydrothermal reaction at 100～180℃ exhibited the similar effect.The comparison experiments showed that BNNDs cannot be functionalized by MPD and OPD,verifying the specific structure of PPD.The potential application of p-BNNDs in latent fingerprints was explored based on their excellent luminescence properties.(3)BNNDs with ultra-long room-temperature phosphorecence(RTP)lifetime and high temperature phosphorecence emission were prepared by introducing fluorine and constructing hydrogen-bond networks.The fluorinated BNNDs(F-BNNDs)exhibited prolonged RTP lifetime of 1.17 s,and the green phosphorescence could be observed by the naked eyes for over 10 s at 25℃ after UV switched off.Unexpectedly,the afterglow was still maintained with lifetime of 2 s at 150 ℃.The results verified the linear relationship between the phosphorescence lifetime and temperature.The fluorination strategy to achieve long-lifetime RTP and high-temperature phosphorescence emission was proved to be effective in three different BNNDs.Based on the great difference in phosphorescence lifetime and phosphorescence wavelengh of BNNDs,their application in anti-counterfeiting and information encryption were explored.