Research On Thick Shell Blue To Near-Infrared InP Quantum Dot Materials And Devices

At present,quantum dots(QDs)have been widely used in LEDs,solar cells,biomarkers,lasers and sensors.In recent years,the synthesis of environmental friendly QDs has been the main goal in the field of QDs.As the InP QDs materials have large exciton Bohr radius,strong quantum confinement effect,and do not contain mercury,cadmium,lead and other pollution elements.It is a new generation of environmental friendly QDs materials.For blue InP QDs,due the bandgap of ZnS is wider(3.68 eV),so we use ZnS as the shell to restrain electrons in the core.By adding excess S-TOP to reacting with unreacted zinc stearate to increase injection efficiency of electrons and holes.At the same time,the ZnS monomer can be formed on the surface of InP/ZnS QDs,which can increase the thickness of the shell and reduce the energy transfer between the QDs.The QY of the pure blue InP/ZnS QDs can reach 45%,and the stability of the QDs can be significantly increased by coating the QDs with SiO2.After 200 hours of blue light irradiation,the efficiency only decreases by 25%.For blue InP QLED,its EQE can reach 1.7%,which reached the highest level reported in the literature.For green InP QDs,we choose ZnMnS alloy as the middle layer to reduce the lattice mismatch between core InP and shell ZnS.The bandgap of MnS is 3.7 eV,which is wider than that of green InP QDs.The electrons and holes in the core are effectively restricted to form type-I structur.Compared with InP/ZnSe/ZnS(type II)QDs,there is no red-shift of PL peak.For InP/ZnMnS/ZnS QDs,QY can reach 80%.By adjusting the halogen ratio of ZnX2 precursor,the minimum and maximum emission peaks are 467 and 620 nm respectively,covering the whole visible light.Elemental analysis by EDX,high-resolution transmission electron microscopy(HRTEM),and X-ray diffraction(XRD)characterization showed that Mn2+was doped in the QDs,and the amount of Mn2+ is determined by ICP-MS.The stability of the QDs was increased by coating the QDs with SiO2.After 200 hours of blue light irradiation,the efficiency of the QDs decreased only 8%.Finally,for InP/ZnMnS/ZnS QLED,its EQE can reach 2.7%.For near-infrared InP QDs,we synthesized large-sized(15 nm)near-infrared InP QDs(>750 nm)by epitaxial growth of InP core,and investigated the effect of temperature on the reaction rate.After epitaxial growth of two hours,the size of InP core increased from 5 nm to 15 nm.Finally,the ligands of QDs are exchanged to obtain water-soluble QDs for application in cell imaging.