Synthesis and characterization of Cd-free InP alloyed Ga nanocrystals for blue emission

Abstract

Quantum dots have property of light emission range from UV to NIR by controlling size. This phenomenon is caused by quantum confinement effect. This property is very useful to apply to light-emitting device. Although Cd-based QDs have remarkable optical properties, Cadmium is toxic and restricted in electrical and electronic equipment by the Restriction of the use of certain Hazardous Substances (RoHS). Cd-based QDs are replaced with Indium phosphide QDs which have 60~80% of QY and have been applied to light-emitting devices. But Synthesis of blue-emitting InP QD has very low PL QY(10% @485nm). In this study, a property that gallium phosphide has larger band gap than InP was used. InP quantum dots were synthesized with Gallium for blue-emitting. Contained Ga was identified by results of XPS and ICP-EDS. InGaP/ZnS core/shell QD had 27% of PL QY at 488nm(excitation wavelength = 450nm) of wavelength and 15% of PL QY at 484nm(sky blue). And InGaP/ZnS was etched depending on amount of dodecanethiol which is used to sulfur precursor and ligands passivation. In addition, This study find that InGaP/ZnS can’t emit real blue-range (<460nm) due to before-mentioned etching process in a condition of this report. Average PL QYs of InGaP/ZnS QDs which were synthesized in this report was 55% at range from 530nm to 647nm. As ratio of Ga to In increased, PL wavelength was shorter and full width half maximum (FWHM) was broader. Size of QDs depended on temperature and amount of oleylamine. The size was larger as the temperature of synthesis and amount of oleylamine increased.