Investigation On The Adjustment Of Photoluminescence Performance Of Carbon Dots And Its Applications

Carbon dots(CDs),as a new type of fluorescent nano-carbon materials,have been attracting attention since they were first prepared.Excellent photoelectric properties and novel structure make it play an important role in the fields of biomedicine,energy storage,and optoelectronic devices.In recent years,the continuous improvement of CDs photoluminescence performance has made researchers pay more attention to the controllable preparation,mechanism analysis,and device development based on CDs.At present,the research on the optoelectronic properties of CDs and the preparation of devices mainly have the following problems:first,due to the wide variety of precursors,it is still difficult to prepare specific photoluminescence CDs by selecting suitable precursors;second,although there have been many studies on the properties of CDs,there are few reports on their structural analysis.In addition,the problem of their fluorescence emission mechanism and the origin of photoluminescence is still vague;third,most of the theoretical calculation-assisted cases are only to establish the carbon core structure(graphite structure),and there are still difficulties in the study of the specific structure of CDs;fourth,although the technology for preparing white LEDs by mixing three-color CDs is mature,the development of high color rendering index white LEDs is still difficult.In response to these urgent problems,this article has areadly conducted in-depth research on the controllable preparation of CDs,fluorescence regulation,mechanism analysis and the preparation of high-quality CDs-based white LEDs.The specific work is as follows:1.Research on the formation process of CDs.Ethanol was selected as the precursor.Under the carbonization of H2SO4,white light emission CDs(W-CDs)were prepared in one step.The W-CDs can be separated and purified into yellow,cyan and blue emission CDs by column chromatography.The experimental results show that the purified three CDs have different polymer and carbon core structures.Through theoretical calculations and experiments,the regulation of the degree of cross-linking and carbonization of CDs on the fluorescence emission has been clarified.Finally,we successfully used these CDs in the preparation of multi-color and white LEDs.2.Controllable synthesis of near-infrared CDs.Precursors with conjugated structure(o-phenylenediamine,dopamine)were selected,and the carbonization of H2SO4 was used to prepare near-infrared emission CDs(685 um).The CDs has a waterphase fluorescence quantum yield of 33.96%,which is the highest value currently reported at this wavelength.Through characterization and analysis of the structure and optical properties of the CDs,it can be found that the main reason of the waterphase near-infrared luminescence is due to the carbonization of H2SO4.Finally,we successfully used CDs in the preparation of red and white LEDs.3.Research on the formation process of full-spectrum emission CDs.Theoretical calculation results show that by controlling the degree and size of graphitization of CDs,the photoluminescence can be adjusted.In view of the fact that ophenylenediamine can produce red CDs under the carbonization of H2SO4,and citric acid can produce blue CDs,we select o-phenylenediamine(sp2)and citric acid(sp3)as carbon sources,just by changing the reaction temperature and pH value,prepared CDs with full-spectrum and excellent two-photon fluorescence emission.Finally,these CDs were successfully used in the preparation of multi-color/white LEDs and discs.4.The origin of red emission of o-phenylenediamine-based CDs.Through the analysis of the above results,it is found that under the carbonization of H2SO4,the addition of dopamine has no obvious effect on the fluorescence emission property.Then,we prepared four red emission CDs under different acid conditions using ophenylenediamine as the carbon source.After purification,these four CDs showed the same fluorescence and absorption,and also had almost the same mass spectra and 1H NMR peak,it can be judged that the source of fluorescence emission of the four CDs is the same.Further theoretical calculations have verified the formation process of CDs and the possible carbon core structure.The experiments in this chapter provide theoretical and practical research on the fluorescence of ophenylenediamine-based CDs,as well as new ideas for the subsequent exploration of the mechanism of other types of CDs.