Photoluminescence spectra revealed broad visible-region emissions attributed to defect-related trap states, with

Zn²⁺ incorporation influencing luminescence intensity. XRD analysis confirmed the nanocrystalline cubic zinc

blende phase of CdS and ZnS, with crystallite sizes in the 10–20 nm range, while SEM micrographs showed

agglomerated yet porous morphologies, offering enhanced surface area. The combined findings highlight the

role of PVA in stabilizing CdS/ZnS nanoclusters, leading to nanocomposites with favorable structural and optical

features. These results underscore the potential of CdS/ZnS/PVA nanocomposites for future applications in

optoelectronic devices, photocatalysis, and electrochemical energy storage systems.

CdS/ZnS nanocomposites; Polyvinyl alcohol (PVA); Quantum confinement; Photoluminescence;

semiconductor (~3.6 eV), offers high stability, non-toxicity, and effective surface passivation when combined

with CdS [4,5]. The integration of CdS and ZnS into heterostructured systems not only enhances photophysical

properties but also suppresses non-radiative recombination through efficient band alignment [6].

Polyvinyl alcohol (PVA), a water-soluble, non-toxic, and biocompatible polymer, has been widely utilized as a

stabilizing and encapsulating matrix for semiconductor nanoparticles due to its excellent film-forming ability,

mechanical strength, and hydroxyl functional groups that facilitate nanoparticle dispersion. Encapsulation of

CdS/ZnS nanostructures in PVA provides structural stability, prevents agglomeration, and allows tuning of

surface states, thereby enhancing the optical and electrochemical performance of the composites [7-9].

Recent studies have demonstrated that CdS/ZnS nanocomposites exhibit superior luminescence, photocatalytic,

and electrochemical characteristics compared to their individual counterparts, owing to synergistic effects and

findings provide insights into the role of polymer encapsulation in modulating the properties of semiconductor

nanoclusters for potential optoelectronic and energy-related applications.

CdS/ZnS/PVA nanoparticles were synthesized via a solution-phase method. A predetermined amount of

cadmium (Cd) was dissolved in ethanol to prepare the Cd precursor solution. Separately, sodium sulfide (Na₂S)

was dissolved in distilled water, and polyvinyl alcohol (PVA) was dissolved in ethanol to obtain the PVA solution.

For the matrix preparation, the Cd precursor was added dropwise into the PVA solution under constant stirring

at room temperature, yielding a transparent and homogeneous PVA–Cd²⁺ solution. Subsequently, the Na₂S

solution was introduced dropwise under continuous stirring, leading to the formation of a yellow-colored

The functional groups and bonding characteristics of the synthesized nanocomposites were examined using a

BRUKER FT-IR spectrometer.

The optical absorption properties of the CdS/ZnS/PVA nanocomposites were measured on a Shimadzu UV-240

spectrophotometer in the wavelength range of 200–800 nm.

The electrochemical behavior of the nanocomposites was investigated using an Origalys SAS France (OGF01A)

instrument. Measurements were performed within a potential window of 100–1000 mV at a scan rate of 30 mV

s⁻¹.

The optical absorption spectrum of the undoped CdS/ZnS/PVA nanocomposites is shown in Figure X. A strong

and sharp absorption peak was observed in the range of 200–220 nm, which can be attributed to the electronic

transition from the valence band to the conduction band within the CdS/ZnS nanoclusters. The position of this

absorption band reflects the combined effect of the wide bandgap of ZnS (~3.6 eV) and the smaller bandgap of

CdS (~2.4 eV). At the nanoscale, band structure modifications occur, and the observed blue-shift relative to the

bulk counterparts confirms the presence of strong quantum confinement.

Fig.1 UV spectra of CdS/ZnS/PVA nanocomposites

A broad absorption tail extending beyond 300 nm was also observed, which can be ascribed to defect states,

confirming the presence of hydroxyl groups from the PVA matrix as well as contributions from adsorbed

moisture. The bands observed at 2930–2850 cm⁻¹ correspond to C–H stretching vibrations of methylene (–CH₂–

) groups in PVA. A distinct band at 1650–1600 cm⁻¹ was attributed to C=O stretching or H–O–H bending

vibrations, suggesting the presence of bound water molecules and possible interactions between PVA and the

nanoparticle surface.

Additional absorptions at 1460–1400 cm⁻¹ and 1370–1320 cm⁻¹ were assigned to C–H bending and O–H bending

vibrations of PVA, respectively. Strong peaks in the region of 1140–1080 cm⁻¹ were associated with C–O–C

stretching and C–O stretching vibrations, further confirming the structural integrity of the PVA polymer matrix.

Importantly, distinct bands appearing in the 690–600 cm⁻¹ region were assigned to Cd–S and Zn–S stretching

vibrations, which validate the successful formation of CdS/ZnS nanoclusters within the PVA framework. The

across the visible region, which is characteristic of nanoscale CdS-based systems.

The observed broadening in the PL spectra can be attributed to trap-state emissions arising from surface defect

states .Upon photoexcitation, electrons are promoted from the valence band to the conduction band of CdS and

subsequently become trapped at defect sites. The recombination of these trapped carriers with holes gives rise

to defect-related emissions. The incorporation of Zn²⁺ ions further modifies the surface trap states, leading to an

enhancement and slight shift of the luminescence band

CdS sample exhibited strong emission peaks at approximately 343 nm and 450 nm in the visible region. While

the peak positions were nearly identical for all samples, notable variations in relative intensity were observed,

suggesting that dopant incorporation and surface passivation influence the recombination dynamics.

The average crystallite size of the nanoparticles was estimated using the Debye–Scherrer equation The calculated

crystallite size was found to be in the range of , indicating the formation of nanosized crystallites.

broad background contribution reflected the semi-crystalline nature of PVA. SEM micrographs revealed

agglomerated but porous morphologies, with nanosized crystallites aggregated into larger secondary structures,

offering enhanced surface area beneficial for electrochemical and optoelectronic applications.

potential of CdS/ZnS/PVA nanomaterials for future applications in optoelectronic devices and electrochemical

energy storage systems.