Preparation And Applications Of Highly Stable CuInZnE(E=S,Se) Core-shell Quantum Dots

Semiconductor nanocrystals（quantum dots）are very good luminescent materials,and their luminous efficiency can reach 100%.Compared with traditional organic fluorescent materials,quantum dots（QDs）have the advantages of high photoluminescence quantum yield（PL QY）,tunable emission wavelength,saturate color and high photochemical stability,which can effectively replace organic light-emitting materials in many areas.At present,the widely applied quantum dots are cadmium-based quantum dots,and the heavy metal ion Cd²⁺belongs to class A pollutants in the industrial standard.Although the surface of QDs can be coated with a shell,the inevitable leakage of Cd²⁺is a potential issue because of its toxicity,and its biocompatibility is poor.As a result,it is difficult for QDs to be scalely applied in biomedical detection,cell and tissue imaging.In order to obtain low toxicity QDs,researchers have paid more attentions to the low toxicity of Ⅰ-Ⅲ-Ⅵ CuInS₂ quantum dots（luminescence range 550nm⁷00 nm continuously adjustable）.and CuInSe₂ QDs（luminescence range 650 nm⁹00 nm continuously adjustable）in recent years.The prepared Ⅰ-Ⅲ-Ⅳ of CuInS₂（CIS）and CuInSe₂（CISe）QDs have been applied in the fields of biological detection,biological imaging and light-emitting diode.However,there are still some problems in the preparation of Ⅰ-Ⅲ-Ⅵ QDs.Ternary I–III–VI QDs prepared as core QDs exhibit poor PLQY and are not stable,and it is often necessary to coat the ZnS shell outside the core to increase its quantum yield.However,due to the continuous cation exchange between Zn²⁺with Cu⁺or In³⁺,and the increase of lattice stress between the core and the shell with the continuous covering of the shell,it is difficult to grow thick shell outside of the CIS or CISe core.This also tend to cause the constantly blue shift of the emission peak of the core-shell QDs and the smaller size particle,and the prepared QDs are“large and not bright,small,bright and unstable”,which further hind the application of Ⅰ-Ⅲ-Ⅵ QDs.In order to prepare high PLQY,high-stability CIS or CISe core/shell QDs,the novel synthisis method has been developed and the prepared QDs were applied in biological detection and quantum dots light-emitting diode（QLED）.The main study contents are as the follows:（1）Preparation of thick-shell CuInZnS/ZnS//ZnS core-shell quantum dots and its application to quantitative detection of C-reactive protein.We have developed a simple new method to successfully prepare high-stability thick-shell CuInZnS/ZnS//ZnS core-shell quantum dots.The average fluorescence PL QY of quantum dots in organic solutions is as high as 77%.The average PL QY of the aqueous phase quantum dots after phase transfer remains at a high level（up to 58%）.After that,we successfully applied the prepared hydrophilic cadmium-free CuInZnS/ZnS//ZnS core-shell quantum dots to the quantitative detection of C-reactive protein in fluorescent labeled lateral flow immunoassay with wide detection range,high sensitivity and minimum detection.The limit of dection（LOD）is 5.8 ng/mL.（2）Preparation of thick-shell CuInZnSe/ZnS//ZnS core-shell quantum dots and their application in QD light-emitting diodes（QLED）.Preparation of high-quality CuInZnSe/ZnS//ZnS core-shell quantum by“one-pot method”for preparing near-infrared quaternary CuInZnSe alloy core and adjusting the thickness of ZnS shell by long-term growth of shell layer and timely replenishment of shell precursor.Then we carried out a series of characterization of the prepared quantum dots.The results show that the thick-shell CuInZnSe/ZnS//ZnS core-shell quantum dots prepared by us have 80%PL QY,wide spectral adjustability and high photochemical stability.In addition,we first applied the prepared thick-shell quantum dots to the QLED construction.The maximum external quantum efficiency（EQE）of 3.0%,4.0%and 2.5%is obtained for the devices based on CuInZnSe/ZnS QDs with the PL peak at 705 nm,719 nm and728 nm,respectively,the turn-on voltage is less than 2 V,which is over 8 times higher than that of CuInSe/ZnS-based QLED and comparable to that of near-infrared devices based on PbS/CdS QDs.