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INTRODUCTION: Cadmium sulfides (CdS) are regarded as a prominent class of
broadband-emitting nanoparticles and contain a direct band gap of 2
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It has
been widely used in light-emitting diodes for flat panel displays and chiefly in photo
chrome–fluorophore assemblage as fluorophores in solar cells [5] CdS Quantum
Dots are the inorganic semiconductors that belong to the cadmium chalcogenide
family
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The Bohr radius of CdS
particles is 5
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CdS nanoparticles or particles with a size smaller than 5
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CdS QDs show 3D
quantum confinement due to their distinct energy levels
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As a result of this quantum confinement, in CdS QDs, the
photoluminescence emission spectrum and the phosphorescence emission
spectrum are produced, which show a sharp and narrow peak, due to the discrete
electronic transitions
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The observation of both photoluminescence and phosphorescence emission spectra
for CdS QDs can provide valuable information about the electronic structure, size,
and properties of the QDs
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The bandgap of bulk CdS is around 2
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Therefore, the absorption peak of bulk CdS is usually
observed in the ultraviolet to the blue region of the electromagnetic spectrum,
around 525-550 nm
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As a result, the absorption peak of CdS QDs is
typically observed in the blue to an ultraviolet region of the electromagnetic
spectrum, around 375-425 nm
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5 eV, which means that they absorb light in the
ultraviolet region of the electromagnetic spectrum
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4 eV, which means that they
absorb light in the blue-green region of the electromagnetic spectrum
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1
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2
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CdS QDs can be synthesized in different crystalline structures, including the facecentered cubic (FCC), hexagonal close-packed (HCP), and wurtzite structures
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Among these wet chemicals, the method is the most
commonly used technique
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They are inexpensive, take less time, and are less hazardous as

compared to other techniques
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CdS QDs have a wide range of potential applications due to their
unique optical and electronic properties
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They have potential applications in imaging,
diagnostics, and therapeutics
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CdS QDs have
potential applications in optoelectronic devices, such as light-emitting diodes (LEDs),
due to their ability to emit light and their high quantum efficiency
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They can be used as photocatalysts to
degrade organic pollutants, such as dyes or pesticides, under visible light irradiation
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CdS QDs can be used as
quantum dots for quantum computing due to their discrete energy levels and ability
to store and manipulate information at the nanoscale
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CdS QDs can release
toxic cadmium ions, which can lead to environmental and health risks
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Some commonly used sources of sulfur for CdS nanoparticle
synthesis include --1
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Sodium sulfide (Na2S)
3
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Hydrogen sulfide (H2S) gas
5
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In the synthesis of CdS
nanoparticles, elemental sulfur is typically reacted with a cadmium source, such as
cadmium acetate, in the presence of a reducing agent and a stabilizing agent
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In this method, Na2S is typically
used as a sulfur source in the reaction with a cadmium precursor, resulting in the

formation of CdS nanoparticles
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Hydrogen sulfide (H2S) gas: H2S can be used as a sulfur source for the synthesis of
CdS nanoparticles in a gas-phase reaction
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The synthesis of high-quality CdS nanocrystals is an active area of research, and
several methods have been developed to achieve this goal such as —
1
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Thermolysis of single precursors at relatively high temperatures
3
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Different types of preparation methods have been developed to control the size
of semiconductor nanocrystals, including cadmium sulfide (CdS) nanocrystals —
a) Size-selective chromatography
b) Size fractionation by exclusion chromatography
c) Stabilizers and polymer
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The two polymorphs have different crystal structures, which affect
their electronic band structures and optical properties
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And the hexagonal form of CdS has a lower
symmetry, which results in a lower density of states at the band edges and a
narrower bandgap
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The hexagonal phase is
thermodynamically stable, which means it has lower free energy than the cubic
phase under normal conditions and the cubic phase of CdS is metastable, which
means that it is not the preferred phase under normal conditions but can be
stabilized under certain conditions
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1155/2009/914501]

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