Preparation And Fluorescence Properties Of Rare Earth Doped Carbon Quantum Dots

Carbon quantum dots are novel carbon nanomaterials which have particle sizes from 1 to10nm.Carbon quantum dots show good properties of low cost,easily preparing,environmental friendly,chemical inertness.These materials have broad spectra and narrow emission spectra,resist photobleaching and blanking,widely used in imaging,sensing and detection.Up to now,Many researches were carried out to amplify fluorescent signals by optimizing experimental conditions and doping other elements.By doping rear earth elements we could also achieve amplification of fluorescent signals,particularly rises in fluorescence intensities and lifetimes.Ionic liquids is entirely composed of anions and cations,existing in liquid phases at room or vicinity temperatures,which is an ideal green solvent to dissolve natural lignin.Carbon quantum dots were synthesized from palm bark and luffa veneer by one step in this experiment,innovatively applying excellent solubilities of green solvent ionic liquids to compose carbon quantum dots with good stabilities and fluorescence properties in a mild and simple way.Then we make use of rare earth complexes to modify the carbon quantum dots composing rare earth doped carbon quantum dots.rare earth doped carbon quantum dots amplify the fluorescence intensity and manage to detect organic pollutants and ions.Study of this paper is as follows:1.A fluorescent carbon quantum dot is prepared in a hydrothermal way at 120℃,with a carbon source of palm bark,sodium hydroxide pre-treated and a solvent of 1-methylimidazolium chloride.fluorescence quantum yield of carbon quantum dots is22.7%;Maximum excitation wavelength of carbon dots is 360nm with a relevant emission wavelength located at 455nm.Fluorescence lifetime is 4.91ns,energy transfer efficiency is28.2%.By using high resolution transmission electron microscope we can find the carbon quantum dots were dispersed uniformly in liquid,which have a particle size range from 1 to4.5nm,average particle size is about 2.65nm.Infrared spectra indicate that there are a large number of carboxyl,hydroxyl and carbonyl groups in carbon quantum dots.2.Lanthanum oxide and citric acid were used to synthesize Lanthanum Citrate complexes,and then mixed with pretreated palm bark to synthesize lanthanum doped carbon quantum dots in one step by a hydrothermal method.The particle size of the prepared La-doped carbon quantum dots ranged from 1 to 9 nm,with an average particle size of about5.4 nm.The maximum excitation wavelength of La-doped carbon quantum dots is 330 nm,the emission peak is 425 nm,the fluorescence yield rises to 31.4%,and the fluorescence lifetime rises to 6.84 ns,energy transfer efficiency is 36.6%.It was found that La-doped carbon quantum dots have characteristic absorption peaks at 270 nm,rich in hydroxyl,carboxyl,carbonyl and other chemical groups.3.After pretreatment,luffa veneer was dissolved in 1-methylimidazole chloride salt.Then yttrium oxide and citric acid were used to synthesize citric acid-yttrium complexes.Then yttrium-doped carbon quantum dots were synthesized by hydrothermal method with the mixtures mentioned above.Fluorescence yield of yttrium-doped carbon quantum dots is increased to 41%,the maximum excitation wavelength is 380 nm,the emission peak is located at 460 nm,the fluorescence lifetime is extended to 7.75 ns,.Obvious lattice fringes can be observed under high resolution transmission electron microscope.The particle size distribution is within 1-10 nm,and the average particle size increases into about 6.6 nm.Infrared spectra show that the carbon quantum dots are rich in more hydroxyl groups,carbonyl groups and carboxyl groups,and own obvious ultraviolet absorption peaks.4.Carbon quantum dots and lanthanum doped carbon quantum dots were used to detect2,4-dinitrophenol respectively.Experiment data show that when the concentration of2,4-dinitrophenol is 25¹00μmol/L,the fluorescence intensity of the carbon quantum dots show a linear relationship with the concentration of the detectors R²=0.97698,I=469.41-1.5441c,and the detection limit is 3.5μmol/L.When the concentration of the detectors is 25¹00μmol/L,fluorescence intensity of the lanthanum doped carbon quantum dots shows a linear relationship R²=0.8925,I=830.6-2.873c,The detection limit increased to1.8μmol/L.5.Carbon quantum dots and yttrium doped carbon quantum dots were used to detect ions.Carbon quantum dots react sensitively to Fe³⁺.When the concentration of Fe³⁺lies in 25¹00μmol/L,the fluorescence intensity shows a linear relationship with the concentration of Fe³⁺ions:R²=0.99439,I=754.5-1.23c,and the detection limit is 4.6μmol/L.Yttrium doped carbon quantum dots are sensitive to the Pb²⁺ions.When the concentration of Pb²⁺ions lies in25¹00μmol/L,the fluorescence intensity shows a linear relationship with the concentration of Pb²⁺ions:R²=0.9909,I=631.46-1.6675c,detection limit increased to 3.5μmol/L.