Preparation Of Zno Quantum Dots And Their Applications

ZnO quantum dots(QDs)have potential applications in the fields of fluorescent ink,bioimaging,and healthy lighting because of their good biocompatibility,adjustable band gap,eco-friendly property,high quantum efficiency and mild synthesis conditions.However,the preparation methods of Zn O QDs are still relatively cumbersome and the yield is low(less than 1 g).Besides,Zn O QDs suffer from fluorescence quenching under acidic conditions and in the presence of metal ions.In this dissertation,for these problems,a route to large-scale synthesis of Zn O QDs has been demonstrated and and over 34 grams of Zn O NP powders can be realized in one synthesis process.On basis of fluorescence quenching of Zn O QDs in the presence of acidic and metal ions,the Zn O can be applied for detection of acid rain,advanced information encryption,repeatable painting.Finally,Zn O QDs were as a spatial carrier to separate carbon dots,and Zn O-carbon quantum dot chains have been realized,which can be used for healthy lighting.The whole dissertation is composed of the following parts:1.Over 34 grams of ZnO QD powders can be realized in one synthesis process.The structure and luminescent properties of Zn O quantum dots synthesized under different conditions were studied in detail.Transient spectroscopy studies found that the light emission mainly comes from surface defects and recombination luminescence of deep level electron holes.The as-prepared Zn O QDs powders were as phosphors to successfully prepare yellow LEDs,which promise the future mass-application of Zn O QDs as low-cost and eco-friendly phosphors for LEDs.2.The fluorescence quenching of the synthesized ZnO QDs under acidic and metallic copper ion conditions was investigated in detail.On basis of fluorescence quenching in different fluorescence quenching mechanisms,some applications have been realized,as follows: Firstly,rewritable painting has been realized.In this process,vinegar and soda were used as eraser and neutralizer,and Zn O QDs solution were used as fluorescent inks.Secondly,the optical properties of Zn O QD and carbon nanodot mixture were studied.We found that The color of the mixture changes from yellow to blue when the p H value is smaller than 5.5,which accords well with the standard p H value of acid rain(<5.6).Zn O and carbon QD mixture is used as dual-emission ratiometric fuorescent sensor to detect acid rain.The results demonstrated provide a visual detection route for acid rain by the naked eye,and thus may be promising for the wide application of acid rain detection in the future.Thirdly,On the basis of such distinct quenching phenomena,a route to advanced encryption has been realized.In this route,Cu Cl2 and vinegar are used as the ink and quencher to generate and conceal the patterns to be enciphered,respectively,on Zn O QD coated paper.3.White luminescent powders consisted of carbon-Zn O alternating quantum dot chains(CZA-QDCs)have been demonstrated by using Zn O QDs as a carrier and silane coupling agents as linkers.On the one hand,the fluorescence quenching of carbon nanodots caused by aggregation has been addressed.On the other hand,Zn O QDs can not only serve as a space carrier but also emit yellow fluorescence,and the white emission was realized by the combination of the yellow fluorescence from the Zn O QDs and the blue emission from the carbon nanodots.The quantum efficiency of the prepared CZA-QDCs is as high as 49%,and the fluorescence can keep stable within 100°C.By coating the powders onto a ultraviolet chip as phosphors,WLEDs with luminous efficiency of 20.1 lm/W,color coordinate,correlated color temperature,and color rendering index of(0.30,0.35),5205 K,and 84,have been fabricated,which provides potential for Zn O-based materials to be used as non-toxic and environmentally friendly phosphors in the future.