الفهرس 
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Abstract
Chalcogenide nanoparticles, particularly those of
group II-VI, are well known with their metastable zinc
blende structure and stable wurtzite structure at high
temperatures. Zinc blende structure is of great importance,
for example in producing branched II-VI semiconducting
nanomaterials such as; bipods, tripods and tetra pods. The
ability to separate between these structures needs an
intensive study on the phase changes in these systems, and
enhancing the stability of their zinc blende phase.
Within this view, Zinc sulfide quantum dots (QDs)
have been synthesized via two methods, one by a simple
non-toxic colloidal reaction of Zn (CH3COO) 2 and Na2S in
the presence of sodium dodecyl sulphate (SDS), acting as an
anionic coordinated capping material, and the second
method is a novel solid–state method of milling of zinc
acetate and thioacetamide (TAA) at different time intervals:
one hour to four hours at low temperature.
A detailed investigation for the structural, optical and
thermal characterization of the synthesized materials using
different techniques including XRD, EDX, TEM, TGA, FT
i
IR, UV-visible spectrophotometer, and photo luminescent
spectrum (PL) led to conclude the main following points:
The particle size can be controllable by adjusting the pH
value in the chemical method and by adjusting the time
of grinding in the solid state reaction. The particle size of
the as-prepared materials lies in the nano-range. The
XRD studies revealed that the synthesized particles have
cubic zinc blende structure with an average size of
5.3±0.2 nm in diameter in case of the chemical method,
and cubic zinc blende structure of different crystalline
sizes for solid state reaction method, where the size for
1, 2, 3 and 4 grinding hours are 4.23±0.039, 3.98±0.48,
3.21±0.75, and 2.95±0.13nm, respectively. Such particle
size values were confirmed with the results of both UVvisible absorption and TEM techniques.
The TEM examination showed uniform spherical distribution.
Results of FT-IR spectra showed possible stretching and
bending modes of ZnS QDs and ZnS interact with
attached Ligands and oxidized into ZnO after heating at
a temperature above 490 oC throughout the investigation
of TGA at different heating rates (5-20 deg/min).
The UV-visible absorption spectrum of the
synthesized ZnS nanoparticles reflects an energy gap of
4.30 eV for the aqueous chemical method.
The UV-visible absorption spectrum of ZnS QDs
milled for 1, 2, 3 and 4 hours in solid state reaction
method reflect an energy gap of 4.24 eV, 4.41 eV, 4.51
eV and 4.60 eV, respectively. These reflect a considerable
blue shift relative to an absorption band edge of bulk ZnS
(3.68 eV at 340 nm) as an indication of size confinement
effect.
The photo luminescent spectrum (PL) of ZnS QDs
exhibited two emissions arising from excitonic and
trapped luminescence can observed at 350 nm and 425 nm
at the excitation wavelengths of 320 nm and 260 nm. The
trapped emission of ZnS QDs shifts to the blue, compared
with bulk ZnS. i.e., to the recombination of electrons at
the sulfur vacancy with holes at the valence band; these
vacancies referred to that these ZnS QDs are suitable for
some potential applications as displays, sensors and/or
lasers.