Synthesis And Charaterization Of Water Soluble Luminescent Nanocomposites

Recently,luminescent semiconductor nanoparticles(NPs),also known as luminescent semiconductor quantum dots(QDs),have attracted considerable attention as novel biological luminescent labels because of the unique optical properties and the latent value of application.Cadmium telluride(CdTe)is one of substances providing very high photoluminescence(PL)quantum effciency amongâ…¡-â…¥semiconductor materials,which could be synthesized in aqueous solution with simplicity and high reproducibility.Especially for fluorescent label applications,the water-soluble NCs are needed.Besides,the surface chemistry plays a great role concerning the properties of the NCs,such as the quantum yield and photostability.So this study mainly focused on the synthesis and surface modification of CdTe QDs. In this paper,CdTe QDs were prepared with different Te sources NaHTe and Na₂TeO₃ in aqueous solution respectively.And the comparison of growth processes and optical properties of CdTe QDs were made.The reflux time,pH of precursor and mole ratio of reagent was discussed respectively to get the optimum reaction condition.In the first synthetic method,the CdTe QDs were prepared in aqueous solution through the reaction between Cd²⁺and NaHTe in the presence of thioglycolic acid as a stabilizer.The molar ratio of Cd²⁺to HTe^- in the precursory solution played an important role in the photoluminescence of the ultimate CdTe QDs.The strongest photo-luminescence was obtained under 4.0 of[Cd²⁺]/[HTe^-]at pH⁸.2 at 100℃for 180 min.In the second synthetic method,the CdTe QDs were prepared in aqueous solution through the reaction between Cd²⁺and Na₂TeO₃ in the presence of L-cysteine as a stabilizer.The molar ratio of Cd²⁺to Te^2-in the precursory solution played an important role in the photo-luminescence of the ultimate CdTe QDs.The strongest photo-luminescence was obtained under 6.0 of[Cd²⁺]/[Te^2-]at 100℃for 55 min.These two methods are low in price,easy to handle,safety and environmental friendly.The method with Na₂TeO₃ as the Te sources is a better approach for the precursor is faster prepared,the higher utilization of raw materials and the better repeatability.The CdTe/Cd(OH)₂ and CdTe/ZnS core/shell nanocomposites were synthesis respectively.The core/shell nanocomposites which had strongest fluorescent intensity were prepared.The size of core/shell nanocomposites was larger than CdTe QDs,which result in the red-shift of fluorescent emission peak and the increase of fluorescent intensity.The growth of inorganic shell was displayed in the photoluminescence spectra of core/shell nanocomposites.It is a simple and usefull way to prove the core/shell structure except the methods of red-shift,size increase and XPS. In addition,the photochemical oxidation of CdTe QDs with cadmium hydrous oxide or zinc sulphide deposition was markedly inhibited.The CdTe/Cd(OH)₂ and CdTe/ZnS core/shell nanocomposites, which have stronger fluorescent intensity,better light stability,and more fluorescence life time,have better vistas than CdTe QDs on applications in the biological luminescent labels,and so on.