Fabrication Of Magnetic-luminescent Nanomaterials Based On CuinS₂/ZnS Core/Shell Quantum Dots And Their Photoluminescence Properties

I-III-VI CuInS2quantum dots (QDs) with a direct band gap (1.53eV of the bulk) areconsidered to be one of the most promising candidates to replace cadmium-based II-VI QDsfor applications in light-emitting diodes, photovoltaic cells, and, in particularly, biomedicallabeling. Because they have high absorption coeffcient, large Stokes shifts, size-andcomposition-tunable photoluminescent (PL) from the near infrared to the visible region, andespecially do not contain highly toxic element，the synthesis of high-quality CuInS2QDs haveattracted great interest. Although the synthesis of CuInS2QDs has been reported, the physicalmodel of luminescence mechanism for CuInS2QDs has not been refined yet. So, it is still ofgreat interest to further investigate the luminescence mechanism of CuInS2QDs. On the otherhand, Cu-Mn-In-S alloy QDs and CuInS2-FePt nanocomposites acted as a new generation ofmagnetic-fuorescent nanomaterials will provide a promising application for biomedicalresearch. Therefore, it is necessary to further analyze the luminescent properties of thesematerials. Based on the above strategies, the original works in this dissertation are given asfollows:(1) CuInS2/ZnS core/shell QDs are synthesized with hot-injection method and their crystalstructure, size, morphology, and luminescent properties are characterized. The obtainedCuInS2/ZnS QDs with the size of about3nm have zinc blende structure, which areindependent on the change in composition. However, the decrease of Cu/In ratio enlarges theband gap of the QDs, which results in the blue-shift in absorption and PL spectra. As the Cu/Inratio decreases from1/1to1/9, the PL quantum yield (QY) and lifetime increase at first andthen decrease. The highest PL QY of44%is obtained for CuInS2/ZnS QDs with an optimum Cu/In ratio of1/6. The PL emission in CuInS2/ZnS QDs is assumed to be radiativerecombinations of carriers from donor-acceptor pairs (DAPs) and from the conductionband-acceptor. The CuInS2/ZnS QDs with Cu/In=1/6show good thermal stability due to higherCu-related defect density, which effectively suppress the thermal activation of carriers. Thepermanent loss of PL intensity for In-rich CuInS2/ZnS QDs is smaller than that of CdSecore/multishell QDs, which is examined through heating-cooling cycling experiments. Theseresults suggest that the PL QYs and thermal stability of CuInS2/ZnS QDs can be adjusted bychanging the Cu/In ratio.(2) The photoluminescence properties of Cu-Mn-In-S/ZnS core/shell QDs were studied.The Cu-Mn-In-S/ZnS QDs with cubic zinc blende and the size of4nm, exhibitmagnetic-fuorescent properties. The experimental results suggest that introducing Mn2+ionsinto CuInS2QDs can induce the PL quenching, red-shift in PL peak, and shortened PL lifetime.The change in PL peak suggests that a new radiative recombination process of carriers isformed due to the introduction of Mn2+ions into CuInS2/ZnS core/shell QDs and the change inPL QYs and lifetime are due to the formation of nonradiative recombination centers inCu-Mn-In-S/ZnS QDs, compared with CuInS2/ZnS core/shell QDs. Moreover, theCu-Mn-In-S/ZnS core/shell QDs exhibit good thermal stability at the temperature from93to270K, which implies that these multinary nanoparticles are more suitable for some specialtechnical applications in solid state lighting and biomedical labeling.(3) The PL quenching and electron transfer of CuInS2/ZnS QDs in blend films with FePtmagnetic nanoparticles (MNs) are studied by steady-state and time-resolved PL spectroscopy.The decrease in PL intensity and lifetime, as well as blue-shift in PL peak are observed in theCuInS2/ZnS-FePt blend films with increasing FePt concentration, demonstrating that electrontransfer occurs from CuInS2QDs to FePt MNs. In CuInS2/ZnS-FePt system, we observe thephotoexcited electrons transfer from conduction band and donor defects including deep andshallow defect states of CuInS2/ZnS QDs to FePt MNs. The two transfer processes of electronsfrom CuInS2QDs to FePt MNs might cause the PL blue-shift. Moreover, the electron transferrate varied with the concentration ratio of FePt MNs to CuInS2QDs，temperature and Cu/Inratio are obtained. It is found that electron transfer rate significantly increases with increasingthe FePt MN concentration and the temperature, as well as with decreasing the Cu/In ratio ofCuInS2QDs. Therefore, the experimental results indicate that electron transfer-induced PL quenching in CuInS2QD and FePt MN blend films should be considered in designing thestructure of magnetic-fluorescent nanocomposites for realizing their highly efficient PL.