Synthesis And Luminescent Properties Of Doped Indium Sulfide Quantum Dots

It is well known from present semiconductor technologies that the incorporation of impurities or defects into semiconductor lattices is the primary means of controlling electrical conductivity, and may also have an immense effect on the optical, luminescent, magnetic, or other physical properties of the semiconductor. It will be imperative to be able to control and understand doping in nanoscale semiconductors if this class of materials is going to evolve into practical applications in electronics or photonics technologies. The remarkable developments on the doped semiconductor nanocrystals will promote the promising applications of this class of materials in wavelength tunable lasing, bio-imaging, and solar cells. Among these semiconductor materials, â…¡-â…¥ doped semiconductor nanoparticles have been extensively investigated. Owing to the Gibbs free energy of the doping reaction, diffusion of the dopant ions and their solid solubility limit, the impurity concentrations attained in experiments are much lower than expected, and for some materials is even zero. In2S3is a semiconductor with a direct bandgap Eg around2.0eV, and have numerous cation vacancies and defects in its lattices. More importantly, In2S3can easily form the alloyed ternary chalcogenide semiconductor nanoscrystals with a variety of metal ions, which makes In2S3an excellent doping candidate to incorporate impurities or defects into its lattices. In this dissertation, we focused on the synthesis of a series of doped In2S3semiconductor nanoscrystals by a hot-injection method. On the other hand, the luminescent properties are also discussed. The detailed contents are as follows:1. Cu:In2S3and Ag:In2S3ternary quantum dots were synthesized by a one-pot hot-injection method. XRD, HRTEM results and PL spectra indicate the incorporation of Cu and Ag into the In2S3lattices. The as-prepared Cu:In2S3and Ag:In2S3possess the compositional homogeneity, high crystallinity and have an alloyed structure. The relative PL quantum yield of Cu:In2S3and Ag:In2S3are up to12%and16%, respectively, which higher than that of CuInS2and AgInS2core.2.(ZnCu):In2S3and (ZnAg):In2S3ternary quantum dots were synthesized by a hot-injection method. XRD, HRTEM results and PL spectra indicate the compositional homogeneity, high crystallinity and the alloyed structure of the as-prepared semiconductors. The key for the successful synthesis of (ZnCu):In2S3and (ZnAg):In2S3was the utilization of an appropriate ratio of OA and DDT as the capping agent, which could suppress the generation of precipitation and the emission of host In2S3, improve the quantum yield, decrease the full width at half-maximum and enhance the optical properties of as-prepared quantum dots. The PL quantum yield of (ZnCu):In2S3is up to40%with tunable emission from450to640nm, and (ZnAg):In2S3have the quantum yield of30%with PL emission from450to700nm.3. Cd:In2S3ternary quantum dots was synthesized by a hot-injection method. XRD, HRTEM results and PL spectra indicate the compositional homogeneity, high crystallinity and the alloyed structure of the as-prepared semiconductors. The PL emission wavelength of Cd:In2S3quantum dots is tunable from450to700nm by varying the Cd content in the nanocrystals with the quantum yield of20%. The growth of ZnS shell on the Cd:In2S3nanocrystals improved their PL brightness and chemical stability, with PL QY up to about60%. The Cd:In2S3nanocrystals across the different compositions exhibiting a large Stokes shift makes it possible to inhibit the reabsorption and Forster energy transfer between the quantum dots. This system provides the alternative in the further applications where high concentrations of nanocrystals are needed.4. Using the OA as the capping agent, white-lighting emission Cd:In2S3ternary quantum dots was synthesized by a hot-injection method. PL spectra indicates that the "growth doping" occurred when the Cd:In2S3shell grew on the In2S3nuclei surface. XRD results demonstrate the as-prepared nanocrystals have the identical crystal structure with the In2S3. The possible reasons of this similarity should mainly drive from the growth doping process, which lead to dopant ions located on the particle surfaces, and the much less dopant ions in the Cd:In2S3shell. Regardless of the variations of the reaction temperature, amounts of Cd and OA in precursors mixture, no Cd:In2S3nuclei were generated at the stage of nucleation. The appearance time of Cd:In2S3could be adjusted by simply changing the reaction conditions, which means that the doping process is decoupled from the nucleation and/or growth by controlling the reaction conditions. By varying the reaction conditions, one can adjust the emission intensity of Cd:In2S3doping nanoparticls, and then produced the white-lighting emission samples.