THESIS
2014
xiii, 54 pages : illustrations (some color) ; 30 cm
Abstract
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...[
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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.
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