Synthesis Of High Quantum-yields CdSe/ZnS、CdSe_xS_1-x/ZnS Core/Shell Quantum Dots And Their Applications To Leds

White light-emitting diodes （WLEDs） show a number of advantages overconventional light, such as high efficiency to convert electrical energy into light,small size, reliability and long operating lifetime, which make them beingpopularly applied in a wide variety of applications, such as lighting and liquidcrystal display. Currently, most commercially available WLEDs emit a bluish, coldwhite light with poor color-rendering properties, caused by that conventionalphosphors are lack of the red and green section. QDs-WLEDs, in which QDs act aslight convert material, are in the spotlight of new optoelectronic materials and havethe potential to replace conventional light. QDs possess high fluorescent quantumyield （QY）, broad absorption spectrum, stability, solution processability, and theiroptoelectronic properties depended on size, composition, and morphology. In recentyears, QDs-WLEDs have been successfully fabricated, and most of them show goodcolor rendering properties but unideal color temperature. It’s still difficult to obtainwhite light with high color rendering index and low correlated color temperature.Another disadvantage of QDs is the fluorescent quenching during the fabricationprocess, resulted from the poor compatability between the surface organic ligandsand epoxy composites. In view of the above, this work discussed the synthesiscondition of multiple-corlors QDs with high efficiency, stability, and fabricationprocess of LEDs, the main research results obtained as follows:（1） In octadecene, adopting CdO as Cd precursor, SeO₂or Se as Se precursorand palmitic acid as ligands, CdSe QDs were synthesized via a hot-injectionmethod and capped by ZnS shell through a facile single-molecular precursorapproach. The effects of Se precursor type, injection temperature, molar ratio ofcadmium and selenium dioxide on the optical properties of CdSe QDs were alsodiscussed, and the optimization synthesis condition was chosen to be SeO₂as Seprecursor,280℃and Cd/SeO₂=1/2, respectively. CdSe/ZnS core/shell QDs werealso synthesized via a facile single-molecular precursor approach. After capping,QYs was largely improved and when growing one monolayer ZnS shell, the QY reached the highest to be33%, caused byindicating the effective passivation ofshell to the surface of core QDs. After being stored in air for one month, the QY ofthe resulting red-emitting QDs was up to50%, indicating their good stability.Moreover, a purple pink QDs-LEDs was successfully fabricated by hybridizingred-emitting QDs/epoxy composites on a blue InGaN chip.（2） To avoid high injection temperature necessary in the traditionalhot-injection method, we developed a hot-injection-like method at a relatively lowinjection temperature （230oC）. In octadecene, composition-controllable ternaryCdSe_xS_1-xQDs with multiple emission colors were obtained via changing the feedratio of SeO₂to S and their emissions almost covered the whole visible region of thespectrum, providing an extremely facile method to synthesize multiple-colors QDs.And then high fluorescent CdSe_xS_1-x/ZnS core/shell （CS） QDs were synthesized bya similar approach to the synthesis of CdSe/ZnS core/shell QDs, and the effect ofZnS precursor quantity on the optical properties were also discussed. As a result,the FL QY of the resulting green （λem=523nm）, yellow （λem=565nm） and red（λem=621nm） emissions CS QDs in toluene reached up to85%,55%and39%,respectively.（3） Red-and green-emitting CdSeS/ZnS core/shell QDs were successfullyapplied to fabricate single-color QDs-LEDs, respectively. Three kinds ofQDs-WLEDs were also fabricated by different color combination. Based onyellow-emitting QDs, a WLEDs was fabricated, and under30mA forward-biascurrent, the correlated color temperature （Tc） was3931K, and the color renderingindex （Ra） was31.3. Another QDs-WLED was fabricated by hybridizing green-,yellow-and red-emitting CdSe_xS_1-x/ZnS CS QDs/epoxy composites on a blueInGaN chip. This four-band RYGB QDs-WLED showed good performance with aCIE-1931coordinates of （0.4137,0.3955）, Ra of81, Tc of3360K at30mA, whichindicated the combination of multiple-color QDs with high fluorescent QYs in LEDa promising approach to obtain warm WLEDs with good color rendering. To avoidthe reabsorption between the QDs, WLEDs was also fabricated by carefullyadjusting the wavelength and matching of red-and green-emitting CdSeS/ZnScore/shell QDs. Under forward-bias current lower than30mA, the Ra was up to90and Tc was between3355K and3653K.