Study Of The Aqueous Preparation Processes And Properties Of Ⅱ-Ⅵ Group Quantum Dots

Quantum dots (QDs) are a kind of fluorescent nanomaterials with good optical properties. The conventional organic methods to synthesize the QDs are usually expensive, environmentally unfriendly and poorly biocompatible. This thesis studied the synthesis of Ⅱ-Ⅵ group QDs via an aqueous route. Aqueous synthesis of CdS QDs in a microporous tube-in-tube micro-channel reactor (MTMCR) was conducted and optimized. High-quality CdTe QDs and the alloys were prepared. The preparation method of CdxZn1-xSe QDs emitting violet to blue light were improved by using a novel reducing agent. All the syntheses were conducted in aqueous phase with a reaction temperature of below 100℃. There was no need to synthesize anion precursors (Se2-, Te2-, etc.) by using Se or Te powders. The main results were as follows:(1) Synthesis of CdS QDs in MTMCR and the improvement of the processesBy using 3-mercaptopropionic acid (MPA)as stabilizer and D-erythorbic acid as oxygen scavenger, Cd source and S source were introduced in to the MTMCR at room temperature to obtain the CdS QDs solution. The CdS QDs obtained emitted light green light, had a cubic crystal structure and a size of 2.7 nm. The as-prepared QDs had many surface defects and a low quantum yield (QY) of less than 3%. Experimental results indicated that flow rates, temperature, micropore size and aging time were the most significant factors to affect the the QDs products. By optimizing the processes, the optical properties of the CdS QDs were improved, with an increase of QY up to 10%.(2) Fast synthesis of high-quality CdTe QDs and CdSexTe1-x alloyed QDs emitting green to red lightCdTe QDs were synthesized at 95℃ in 30 minutes by using mercaptosuccinic acid (MSA) as the stabilizer. The sizes of the QDs were manipulated by only changing the hydrazine concentration, resulting in an emission range of 512-650 nm and a highest QY of 55%. By changing material ratios, orange-red emitting CdTe QDs with a QY of 30% were obtained. The as-prepared QDs had sizes of 2.6-4.3 nm and were characterized by XRD as zinc blende crystal structure. CdSexTe1-x alloyed QDs were also synthesized with a similar method in 45 minutes and the emission range extended to a near-infrared area of 750 nm.(3) Synthesis of violet to blue emitting CdxZn1-xSe QDsIn order to obtain anion precursor fastly, Na2SeO3 was reduced to give Se2- using NH2OH-HCl and NaBH4 as reducing agents. CdxZn1-xSe QDs were synthesized by using N-acetyl-L-cysteine (NAC) as the stabilizer with heating at 98℃ for 4.5 h. The emission range of the CdxZn1-xSe QDs was 415 nm (pure violet)-466 nm (bright blue). The as-prepared QDs had less defects and good visual effect, and they had a considerable QY of about 6-10%.