| Fluorescent carbon dots(CDs),a kind of carbon materials,have received increasing interest since they were first found in 2004.Having many peculiar properties,such as high water solubility,tunable emission,low toxicity,and facile preparation,CDs show great value for their applications in many fields including biological imaging,cancer treatment,sensor,photoelectric devices and catalytic.Though various precursors and methods have been applied on the preparation of CDs,most of the products show blue-light-region emission.To realize high-efficient fluorescent CDs of emission at longer wavelength,researches on regulating fluorescence of CDs under controlled,comparable conditions are in great desire.Furthermore,there is no unified view upon the fluorescence mechanism of CDs by now.Many researchers proposed that the surface state of the CDs is an important factor affecting their fluorescence behaviors.It is very practical to analyze the relationship between surface functional groups and luminescence properties of carbon dots for further guiding the synthesis of fluorescent carbon dots.In this paper,using a facile hydrothermal method,high performance fluorescence carbon dots with uniform morphology were obtained from aromatic compounds.We firstly prepared efficient yellow-green emissive CDs using three phenol derivatives.At the same time,the relationship between the fluorescence properties and the surface states of carbon dots was investigated.What is more,blue-yellow dual-emissive CDs with wide color gamut were synthesized using phenylenediamine as a surface modifier.The above mentioned CDs were used as color conversion layer to fabricate white light emitting diodes,suggesting the bright future of carbon-dots-based light emitting diode.The thesis'main works are as follows:1.Ethylenediamine and three different carbon sources:hydroquinone,phenol and 4-(2-pyridylazo)resorcinol were adopted in the hydrothermal synthetic processes of the CDs.Three efficient yellow-green emissive N-doped CDs of the same fluorescence peak wavelength but different photoluminescence quantum yields(PLQY)were realized through a facile hydrothermal method.The as-prepared CDs exhibit not only excited-independent emissions but also similar surface states.The CDs prepared from 4-(2-pyridylazo)resorcinol have the highest PLQY of 24.4%(in water,and 53.3%in ethanol)among the three CDs.And this is ascribed to the high nitrogen content and abundant surface functional groups of the CDs.After washing and reducing these prepared CDs which have similar surface states,the emission evolution was studied linking the surface defects and the changes of surface bonds.The fluorescence can certainly be attributed to the surface of the carbon dots,and the surface states control the photoluminescence features.2.Using ascorbic acid as carbon source and p-phenylenediamine as surface modifier,blue-yellow dual-emissive CDs were prepared.Such carbon dots show unique emission band almost extends the entire visible region with quantum yield of 20%.A series of experimental research was conducted for optimal performance(broad color range).Under excitation of 350nm,the as-prepared CDs exhibit a wide emission peak from 400nm to 700nm,with an attractive full width at half-maximum(FWHM)up to 170nm.3.Both of the best-performance CDs in work 1 and work 2 were used to fabricate two white light emitting diodes(WLED).Firstly,we employed the best CDs in the three samples of work 1 to serve as a yellow-green color conversion layer in the fabricating of WLED,the prepared WLED shows bright light with a high color rendering index up to 93.3.After that,the blue-yellow dual-emissive CDs which can give white light were used to be the only color conversion layer to fabricate a WLED.Having a CIE color coordinate of(0.2851,0.3210),and a CRI up to 83.5 at 100 mA,the as-prepared light emitting diode exhibits a wide emission in the electroluminescence spectrum,implying the bright future of CDs in lighting and display fields. |
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