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This research investigates the impact of copper doping on the structural and morphological properties of CdS nanocrystals produced through a chemical synthesis process. The study utilized X-ray diffraction (XRD) to analyze various parameters such as crystallite structure, size, interplanar space, lattice parameters, and volume of the unit cell. The results showed that copper incorporation increased the average crystallite size of the nanocrystals, and XRD confirmed the hexagonal wurtzite structural phase of both prepared CdS and copper-doped CdS nanocrystals. Field emission scanning electron microscopy (FESEM) was also used to analyze the nanocrystals' surface, shape, and size, which revealed a smooth surface, spherical shape, and nano-size range. Moreover, Energy dispersive X-ray spectroscopy (EDAX) analysis, along with FESEM mapping studies, demonstrated a uniform distribution of individual elements. These findings provide valuable insights into the potential applications of copper-doped CdS nanocrystals in various optoelectronic fields.

This study synthesized Cu-doped CdS nanoparticles using the chemical sol-gel method[11], a simple and cost-effective technique for producing nanoparticles. Various characterization techniques such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX) were used to analyze the synthesized nanoparticles.

Semiconductor nanoparticles, such as CdS nanoparticles, possess unique optical and electronic properties that interest researchers particularly [5]. Doping the nanoparticles with metals or other elements, these properties can be further modified. Doped CdS nanoparticles have gained significant attention due to their luminescent characteristics[6], which can be influenced by impurity states introduced through doping. The electronic and optical properties of the semiconductor can be tuned through doping, making these nanoparticles highly suitable for a range of applications. Luminescent nanoparticles, such as doped CdS nanoparticles, have several potential applications in various fields[7]. In bioimaging, luminescent nanoparticles can be used as imaging agents to detect and monitor cellular processes or disease states in living organisms. In photovoltaic devices, these nanoparticles can be used as absorbers or charge transport layers to improve performance. Luminescent nanoparticles are also used in light-emitting diodes (LEDs), emitting light when an electric current is passed through them[8-10].

In this experiment, Cadmium chloride (CdCl2), Thiourea (CH4N2S), Copper sulfate (NiSO46H2O), and Sodium hydroxide (NaOH) are used as the precursors of cadmium, sulfur, and copper. Pure CdS and Cu-doped CdS nanocrystals are synthesized by the chemical co-precipitation method. The step-by-step synthesis process is shown in the following figure 1.

Fig.1.Schematic Diagram of the Synthesis Process.

Characterization Techniques

The structural properties of Cu-doped CdS nanoparticles were analyzed using a Rigaku 600 Miniflex X-ray diffractometer, which detected nanoparticles at 3°/m within the range of 20 to 60°. The X-ray diffraction pattern provided information on the synthesized nanoparticles' crystal structure and lattice parameters. The nanoparticles' surface morphology and doping confirmation were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. The SEM analysis provided information on the nanoparticles' size, shape, and distribution, while EDX confirmed Cu doping in the CdS lattice.

Crystallographic Analysis

Fig. 2. XRD patterns of CdS and Cu-doped CdS

In this study, X-ray diffraction curves of CdS and 5 wt.% Cu-doped CdS nanoparticles were analyzed and are shown in Fig. 1. The diffraction peaks observed at angles 2θ ~ 25.53, 26.82, 29.92, 37.63, 44.25, and 52.21 for CdS, and 2θ ~ 24.99, 26.67, 28.10, 36.84, 43.93, and 52.10 for Cu-doped CdS correspond to the (100), (002), (101), (111), (102), (110), (103) and (112) planes. These peaks indicate the hexagonal wurtzite structure of the CdS nanoparticles, as confirmed by comparison with standard data (JCPDS, Card no. 41-1049) [12].

Cu doping in CdS increased the intensity of the peaks and increased the average crystallite size of the nanoparticles. Debye Scherer's[13] formula was used to estimate the average crystallite size, which was found to be 5.5139 nm for CdS and 21.6433 nm for Cu-doped CdS. The lattice parameters a and c were also observed to increase with Cu doping in CdS, as presented in Table 1.

Moreover, the nanoparticles' average dislocation density and strain were estimated and found to be 0.5157×10-3 and 0.0025×10-3, respectively, for CdS, and 11.5692 and 0.0016, respectively, for Cu-doped CdS[14].The estimated structural parameters are summarised in Table 1.

Surface morphology and Elemental Analysis

The FESEM mapping and EDX spectra shown in Fig.2 provide insights into the elemental composition and surface morphology of CdS and Cu: CdS nanostructures. The mapping shows the presence of cadmium and sulfur in pure CdS and the additional presence of Cu in Cu: CdS nanocrystals, indicating successful doping. The SEM image of the nanostructures reveals different grain sizes and accumulation in the Cu-doped CdS compared to the pure CdS, consistent with the XRD analysis. The agglomeration effect may be due to the surface effect of the nanoparticles. These results suggest that Cu doping has a minor effect on the grain size and morphology of the CdS nanocrystals.

Element	CdS		Cu: CdS
	Weight %	Atomic %	Weight %	Atomic %
S	10.947	30.114	14.877	36.916
Cd	89.053	69.886	79.923	56.573
Cu	--	--	05.200	06.511

Table .2. Weight and Atomic Percentage of Elements present in CdS and Cu:CdS

The research has successfully demonstrated the potential of copper-doped CdS nanoparticles for use in various optoelectronic applications. The study has shown that incorporating copper into CdS nanocrystals can significantly modify their structural and morphological properties, thereby altering their optical and electronic characteristics. The findings of the study suggest that the addition of copper to CdS nanocrystals can result in changes in their crystal structure, size, and shape, which can affect their optical and electronic properties. The formation of CuS-CdS heterojunctions due to the presence of Cu can lead to a redshift in the absorption edge of the nanoparticles. This shift in the absorption edge can be exploited in various applications such as photovoltaic devices, photoelectrochemical cells, and optoelectronics. The study also suggests that further improvements in the properties of CdS nanocrystals can be achieved by selecting appropriate proportions of transition metal dopants. This finding indicates that optimizing doping concentrations and ratios could lead to the development of CdS nanocrystals with improved properties that are highly suitable for various optoelectronic applications. Overall, the research provides valuable insights into the potential of copper-doped CdS nanoparticles as a promising material for various optoelectronic applications. The findings of this study could be useful for researchers working in the field of nanotechnology and could contribute to the development of new and innovative technologies for various applications.

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