Synthesis Of Quantum Dots In Aqueous And Their Application For White Leds

Quantum dots (QDs) were synthesized in aqueous medium. The properties of these QDs were investigated. The crystalline structure, component, size, and optical properties of these QDs were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Energy Dispersive Spectrometer (EDS), UV-Vis absorption (UV-Vis) and photoluminescence spectrum (PL), respectively.The results show that:(1) The obtained cadmium selenide (CdSe) QDs using TGA as stabilizer, and SeO2as Se source, with yellow light-emitting, displayed a broad excitation band, The as-synthesis CdSe was zinc-blended structure, approximately spherical, and good photooxidation resistance.(2) The CdSe host nanocrystals (NCs) doped with Eu ions have been synthesized in aqueous using thioglycollic acid (TGA) as stabilizer. Their structures, elements, shape and spectral properties were studied. The obtained nanocrystals were consistent with the zinc blende CdSe crystal structure, with approximately spherical aspect. It is found that the resulting Eu-doped nanocrystals show a broadband emission peak at-505nm determined by photoluminescence (PL) measurements, exhibited the Eu-related luminescence. The UV-Visible (UV-Vis) studies show Eu-doped CdSe nanocrystals showed blue shift with respect to the bulk value, and had a obvious absorbance at-450nm,(3) By employing a novel selenium source Sodium Hydrogen Selenite (NaHSeO3), we demonstrate that relatively narrow photoluminescence (PL) band with foll width of half-maximum (FWHM) down to44nm,3-mercaptopropionic acid-stabilized cadmium selenide (CdSe) quantum dots (QDs) can be conveniently prepared in aqueous phase. The obtained CdSe QDs show high PL in the yellow spectral range, and with a high quantum yields (QYs) reach a maximum value of9.3%. The influence factor of molar ratio of Se/Cd for this approach was also discussed.(4) The alloy CdSexTe1-x quantum dots (QDs) have been synthesized in aqueous, the3-mercaptopropionic acid (3-MPA) capped CdSexTe1-x QDs had stable luminescence properties with maximum wavelength range from500nm to720nm, and the maximum quantum yield reach28%, and the absorbance wavelength range from460nm to700nm, XRD results showed that the obtained CdSexTe1-x QDs were of zinc-blended crystal structure and approximately spherical with an average sizes about4-6nm.(5) White light-emitting diodes (white LEDs) were fabricated by coating the CdSe samples onto a460nm-emitting InGaN chip. Both samples exhibited good white balance, the three CdSe based-white LEDs with low color rendering index (CRI) equal to40.5,49.3,43.6, respectively. And the CRI of the CdSe/CdS QDs based-white LED was77.1. Indicating the as-prepared CdSe/CdS QDs was a good alternative for White LED application. White LEDs based on CdSexTe1-x/ZnS QDs, commercially known as YAG:Ce, and hybrid phosphor of CdSexTe1-x/ZnS QDs and YAG:Ce, were fabricated. The luminescent properties of the resultant white LEDs were evaluated. The CdSexTe1-x/ZnS QDs based-white LEDs with a highest CRI of73.5. The higher red-component in the emission spectrum from CdSexTe1-x/ZnS QDs increased the CRI value of the commercial YAG:Ce-based white LEDs from62.6to83.3.