Synthesis Of Highly Efficient Mn Doped GdS Quantum Dot And Their Optical Properities

Luminescent semiconductor nanocrystals (NCs, or named quantum dots: QDs) have been recently received considerable interest because of their unique physical and chemical properties, such as quantum-size effect, dielectric confinement effect, and surface effect et al., which makes them be promiseing to be utilized in optoelectronic and biomedical devices. Recent researches revealed that NCs doped by transition metal ions could not only retain nearly all intrinsic advantages of QDs, but also possess additional merits such as large Stokes shifts (to avoid self-absorption/energy-transfer), enhanced thermal and chemical stabilities, and long excited state lifetimes. These make the transition metal doped QDs become one of the hot and active topics in this field. In present work, we focus on the synthesis of Mn doped CdS QDs via the nucleation-doping strategy, which aims to obtain the material for the exploration of LEDs with highly efficient and well-resolved Mn2+ion emission. The relationship between optical properties and structures of QDs, and the energy transfer process between QDs and1,3,5-tris(N-phenylbenz-imidazol-2,y1) benzene (TPBI) in QD/TPBI blend films have been investigated systematically. Based on the work as mentioned above, the main results can be drawn as bellow:(1) Mn doped CdS QDs with a well-defined core-shell structure of MnS/ZnS/CdS were fabricated via the nucleation-doping strategy. It indicates that the designed interface buffer layer of ZnS plays a significant role on the formation of hightly efficient Mn:CdS QDs. The as-synthesized MnS/ZnS/CdS QDs exhibit extremely higher photoluminescence quantum yield (PL QY)(up to68%), which is two times more than the highest one of Mn2+ion doped cadmium based II-VI semiconductor QD ever reported. The photoluminescence (PL) of the QDs consists of well-resolved Mn2+ion emission without any detectable emission from the CdS band edge or surface defects.(2) The ligands exchange process of MnS/ZnS/CdS QDs is optimized for the improvement of charge injection and energy transfer. Changing the long carbon chain oleylamine (OLA) to short-chain benzylamine (BLA) has little influence on the QDs’PL QY (from68%to66%). It is expected that the hold facility of the QDs’PL QY could enhance the energy transfer efficiency with the electron transport materials and also can favor the study of the follow-on device. Oleylamine has been replaced by water-soluble mercaptopropionic acid on the surface of QDs and the PL QY is still46%, which can establish the foundation of the future biology/biomedicine applications.(3) The investigation on the thermostability of the MnS/ZnS/CdS QDs with various CdS shell thicknesses demonstrates that the PL intensity of QDs with a thick CdS shell is almost unchanged in the temperature range of80to360K, suggesting the high thermal stability of our QDs as compared to the common types of undoped QDs.(4) The energy transfer between QDs with different shell thicknesses and TPBI in QD/TPBI blend films has been investigated. The results imply that an efficient energy transfer from the donor (TPBI) to the acceptor (QD) has been achieved, according to the phenomenons of shortened PL lifetime of TPBI and enhanced PLE within the QDs. Meanwhile, the energy transfer efficiency has been profoundly improved with the increase of the shell thicknesses.