Synthesis, Optical Property And Film Assembly Of Highly Efficient Semiconductor Quantum Dots

In this thesis, highly efficient semiconductor CdTe quantum dots (QDs) with tunable emission wavelengths were successfully synthesized via a low temperature solution route. The influences of preparative conditions and surface stabilizers on the optical properties of CdTe QDs were systematically investigated. Through adjusting the preparative conditions (temperature, time and pH) and surface stabilizers (mercaptoacetic acid and L-cysteine), highly efficient CdTe QDs with emission wavelength adjustable in range of 500-650 nm were obtained. Meanwhile, highly efficient blue emitting ZnSe QDs with emission wavelength at 410 nm were successfully achieved as well via the low temperature solution route. The obtained blue, green, red emitting semiconductor QDs showed highly efficient luminescence and could be used as key materials for optical films assembly and LED construction. By employing the layer-by-layer (LBL) assembly technique, the CdTe and ZnSe semiconductor QDs were assembled into functional optical films with film thickness tunable in nanoscale, and the blue, green, red and full color emitting semiconductor QD optical films could be fabricated. The assembly behaviors, surface topologies and optical properties of the obtained QD optical films were systematically studied. The semiconductor QD optical films show a great potential for application in miniaturized semiconductor QD LEDs.In the first chapter, the general concepts, synthesis, properties and application of semiconductor QDs were reviewed. Based on the previous works and research frontiers of semiconductor QDs, the ideas for research of this thesis was presented.In the second chapter, highly efficient semiconductor CdTe QDs with tunable emission were prepared via a low temperature solution method by using mercaptoacetic acid (TGA) and L-cysteine as surface stabilizers according to the reported methods with slight modification. The optical properties of the CdTe QDs were characterized by UV-visible Spectroscopy and Fluorescent Spectroscopy. The influences of surface stabilizers, reaction time and temperature, and pH on optical properties of CdTe QDs were carefully studies. By utilizing proper surface stabilizer and optimizing preparative conditions, a series of highly efficient CdTe QDs with emission wavelength adjustable in range of 500-650 nm were obtained. Highly efficient semiconductor ZnSe QDs were also prepared via this low temperature solution method by using mercaptoacetic acid (TGA) as surface stabilizer. The optical properties of the ZnSe QDs were characterized by UV-visible Spectroscopy and Fluorescent Spectroscopy.In the third chapter, the functional optical films constructed by alternative deposition of positively charged quaternary ammonium ion cationic starch (QAICS), poly(diallyldimethylammonium chloride) (PDDA) and negatively charged CdTe, ZnSe QDs were fabricated on different glass substrates via LBL assembly technique. In particular, the new use of quaternary ammonium ion cationic starch (QAICS) for construction of QAICS/QD films was demonstrated, and the QAICS/QD optical films exhibiting efficient blue, green, red and full color luminescence were successfully realized by LBL assembly, which showed dense, smooth and efficient luminous features similar to the films constructed by LBL assembly of PDDA/QDs. The optical properties of the films were studies by means of UV-visible Spectroscopy, Fluorescent Spectroscopy, Scanning Electron Microscopy, Atomic Force Microscopy and Confocal Fluorescence Microscopy. The optical films showed very bright emitting colors under UV irradiation, even brighter in comparison with their corresponding quantum dot aqueous colloid solutions. The assembled optical films provide the prospect of miniaturized semiconductor light-emitting-diode applications.In the fourth chapter, the construction of LED devices based on the functional optical semiconductor QDs films was attempted by sandwiching PDDA/CdTe QD films between indium-tin-oxide (ITO) and magnesium or aluminum electrodes with glass substrates covered by an indium-tin-oxide (ITO) layer as the anode contact, magnesium or aluminum as cathode contact, and PDDA/CdTe QD films as light-emitting layers. The electroluminescence of the constructed LED devices is under investigation.In summary, highly efficient semiconductor QDs were synthesized, and semiconductor QD optical films were fabricated via layer-by-layer assembly technique. In addition, the construction of LED devices based on semiconductor QD films was attempted. The obtained semiconductor QDs and optical films may find potential application in optoelectronic devices.