Zhongping Zhang

Synthesis of high quality and stability CdS quantum dots with overlapped nucleation-growth process in large scale

A low-cost, green, and reproducibly non-injection one-pot synthesis of high-quality CdS quantum dots (QDs) is reported. The synthesis was performed in the open air by mixing precursors cadmium stearate and S powder into a new solvent N-oleoylmorpholine. An overlapped nucleation-growth stage followed by a dominated growth stage was observed. The resulting QDs exhibited well-resolved absorption fine substructure and a dominant band-edge emission with a narrow size distribution (the full width at half maximum (fwhm) was only 22-24nm). The maximum photoluminescence (PL) quantum yield (QY) was as high as 46.5%. Highly monodispersed CdS QDs with tunable sizes and similar PL fwhm and QYs could also be obtained from the CdS QDs in a large-scale synthesis. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs with high crystallinity had a cubic structure. A significant PL improvement and a continuous QY increase for the CdS QDs were observed during a long storage time in air and in a glovebox under room temperature. A slow surface reconstruction was proposed to be the cause for the PL enhancement of CdS QDs.

A Phosphine-Free Route to Size-Adjustable CdSe and CdSe/CdS Core–Shell Quantum Dots for White-Light-Emitting Diodes

The selenium dioxide was used as the precursor to synthesize wide-size-ranged CdSe quantum dots (2.4-5.7 nm) via hot-injection route. The CdSe quantum dots are featured with high crystalline, monodisperse, zinc blende structure and wide emission region (530-635 nm). In order to improve the stability and quantum yield, a phosphine-free single-molecular precursor approach is used to obtain CdSe/CdS core/shell quantum dots. The CdSe/CdS quantum dots are highly fluorescent with quantum yield up to 65%, and persist the good monodispersity and high crystallinity. Moreover, the quantum dots white light-emitting-diodes are fabricated by using the resultant red emission core/shell quantum dots and Y3Al5O12:Ce3+ yellow phosphors as color-conversion layers on a blue InGaN chip. The prepared light-emitting-diodes show good performance with CIE-1931 coordinated of (0.3583, 0.3349), an Ra of 92.9, and a Tc of 4410 K at 20 mA, which indicate that the combination of red-emission QDs and yellow phophors as a promising approach to obtain warm WLEDs with good color rendering.