The Synthesis Of Non-Cd System Quantum Dots And The Application

The unique photoluminescence (PL) and electroluminescence (EL) properties of inorganicsemiconductive quantum dots (QDs) make them important for both fundamental research and industrialapplications, such as light-emitting diodes (LEDs), lasers, biomedical labeling, etc. Thus，much effort hasbeen devoted to synthesize different kinds of semiconductor NCs. But most of those NCs containheavy-metal or rare-metal cations such as cadmium, lead, mercury and indium.However, there are growing concerns regarding the risks that these materials pose to our health and tothe environment, as well as most recent reports reveal that the applications in biological field require NCshave strongly emitting, low toxicity or nontoxic (free of heavy-metal cations, such as cadmium, lead, andmercury), and preferably emission in the visible to near-infrared range with good photostability. Especiallybecause of their high quantum efficiency, highly saturated color, and simple color tunability in the solidstate compared to those of conjugated molecules (polymers) or inorganic phosphors, QDs are consideredone of the most promising emitters for next-generation displays and solid-state lighting.With the renovating of synthetic methods, QDs with high quantum yields (QYs) have beencontinuously developed, and their corresponding performances of QD-LEDs have been improvedrapidly.Now, the highest luminance of red emitted QD-LEDs can reach up to50,000cd/m2, and theexternal quantum efficiency (EQE) can reach above18%. The green QD-LEDs also show a brightness over200,000cd/m2with EQE of5.8%. All of those values are comparable with state-of-the-art organiclight-emitting diodes (OLED) technology. In recent years, the preparation of QD-LED has made greatprogress, but in some parameters, compared to OLED which has been used on the market, such as QD-LED luminous efficiency on the part of the light zone, still needs to be improved. Meanwhile, in thepast two decades, much effort has been devoted to synthesize different kinds of semiconductor NCs. Butmost of those NCs contain heavy-metal or rare-metal cations such as cadmium, lead, mercury and indium,which make up the core or shell (often both) of colloidal QDs. However, there are growing concernsregarding the risks that these materials pose to our health and to the environment, or some of them will bein shortage. Recently, severe limits for the use of these materials in consumer electronics have been clearedby the European Union’s Restriction of Hazardous Substances Directive. All place the heavy/rare-metalcontained NCs in a disadvantageous position or even in a doubtful future for applications in the field ofbioimaging, light-emitting devices, and solar cells.Therefore, how to synthesis of high-quality heavy/rare-metal-free NCs and to explore NC emittershaving such required properties is of great important.Based on the above, we have done the work as following:(1)Because of a highly match of lattice parameter and almost consecutive change of lattice parametersfrom CuInZnxS2+xcore to ZnS shells, the structure of CuInZnxS2+x/ZnS core/shell can largely reduce theformation of structural defects, so we choose CuInZnxS2+xas core and ZnS as shell. The relative PLquantum yields (QYs) of CuInZnxS2+xNCs could reach up to30%, with tunable emissions in580–780nm.Then, CuInZnxS2+x/ZnS core/shell NCs were synthesized and showed greatly improved optical properties,the PL QY of the CuInZnxS2+x/ZnS NCs can reach up to60%. Even in the near-infrared region, the PL QYstill can achieve up to45%due the successful controlled red shift of PL during the ZnS shell growthprocess. More importantly, such core/shell NCs can be transferred into water successfully usingamphiphilic oligomer (polymaleic acid n-hexadecanol ester) as surface coating agent by anorganic-aqueous phase transfer method and the PL QYs can be well controlled over40%, and a biosensor system (lateral flow immunoassays system, LFIA) for the detection of C-Reactive protein (CRP) wasdeveloped.(2)Highly violet-green (from400nm to520nm) emissive Al2S3nano fluorescent material weresuccessfully synthesized by facile colloidal method, With narrowest full width at half-maximum (fwhm) of42nm and photoluminescence (PL) quantum yield (QY) of48%. More importantly, such nanofluorescent material have high stability and can keep high PL quantum yield in the process of ligands loss.