Quantum dots (QDs) are one category of nanoparticles or nanocrystals, which are semiconducting materials with diameters in the range of 2-10 nm. QDs possess the distinctive optical and electronic properties as a result of quantum confinement effect, which results from the tiny particle size that is smaller than Bohr radius. Therefore, QDs exhibit a remarkable fluorescence property, which enables QDs to produce distinctive colors that are determined by the particles size. Moreover, QDs have the merits, such as the wide wavelength range, narrow emission spectra and the application of non-rare earth elements. As such, QDs have the potential applications in many fields including biology sensors, displays and LED industry.

The primary objective of this work is to find a convenient an...[ Read more ]

Quantum dots (QDs) are one category of nanoparticles or nanocrystals, which are semiconducting materials with diameters in the range of 2-10 nm. QDs possess the distinctive optical and electronic properties as a result of quantum confinement effect, which results from the tiny particle size that is smaller than Bohr radius. Therefore, QDs exhibit a remarkable fluorescence property, which enables QDs to produce distinctive colors that are determined by the particles size. Moreover, QDs have the merits, such as the wide wavelength range, narrow emission spectra and the application of non-rare earth elements. As such, QDs have the potential applications in many fields including biology sensors, displays and LED industry.

The primary objective of this work is to find a convenient and effective method that modifies the surface of QDs. This modification makes the QDs, such as zinc oxide (ZnO), greatly improve the stability and quantum yield.

The surface modification of ZnO QDs was synthesized through in-situ sol-gel method. Fourier Transform infrared spectroscopy (FTIR) was used to detect the functional groups of as-prepared QDs and the result showed that the silane functional groups were successfully grafted on the surface of ZnO QDs. The result of X-ray diffraction (XRD) proved that only the surface of ZnO QDs was modified with the functional groups while the crystal structure of ZnO QDs was preserved during the modification process. Transmission electron microscope (TEM) images revealed that the surface modified ZnO QDs had a smaller particle size and better dispersion than the pristine ones. A software (Nano Measurer) was utilized to quantify TEM results and gave the general results of particles sizes and deviation. From the photoluminescence spectra, surface modified dots had a smaller full-width-at-half-maximum (FWHM) and higher peak intensity than the pristine dots. Quantum yield was calculated for pristine and surface modified dots, respectively. It turned out that quantum yield of modified ones increased 5 times than that of pristine dots. From the digital images, three groups of dots emitted different colors in a wide range, from blue to yellow. More significantly, the surface modified dots had better stability which could be optically transparent for more than 12 weeks with slightly difference in the photoluminescence spectra.