INFLUENCE OF PRECURSOR CONCENTRATION ON STRUCTURAL AND MORPHOLOGICAL CHARACTERISTICS OF ELECTROCHEMICALLY SYNTHESIZED CDS NANOCRYSTALS
DOI:
https://doi.org/10.32782/pet-2025-2-13Keywords:
nanocrystals, electrochemical synthesis, X-ray diffraction, morphology, phase composition, second harmonic generationAbstract
The paper presents the results of a comprehensive study on the influence of sodium chloride concentration in the electrolyte on the structural, morphological, and nonlinear optical properties of cadmium sulfide (CdS) nanocrystals. A2B6 semiconductor compounds are promising materials for modern optoelectronics and photonics due to unique physicochemical properties arising from quantum confinement effects. The synthesis of nanostructures was carried out by electrolysis of an aqueous solution containing thiourea and sodium chloride, using a soluble cadmium anode. The process was conducted at a temperature of 363 K and a constant current density of 0.192 A/cm2. A key feature of the work is the analysis of the NaCl concentration influence in a wide range from 0.2 to 2.0 M on the formation of the precipitate crystal structure. Using scanning electron microscopy (SEM), it was established that the synthesized nanocrystals possess predominantly flake-like morphology. Size analysis revealed the polydispersity of the samples: the particle diameter varies within 5–70 nm, with an average size of 35–40 nm, and the flake thickness is 5–25 nm. An important experimental result is that the change in precursor salt concentration does not exert a significant influence on the average geometric parameters of nanoparticles, indicating the stability of nucleation mechanisms under the chosen conditions. X-ray diffraction (XRD) showed that all obtained samples are two-phase systems containing a mixture of metastable cubic phase (sphalerite) and thermodynamically stable hexagonal phase (wurtzite). A nonlinear dependence of the phase composition on NaCl concentration was revealed: the content of the acentric wurtzite phase varies within 74–90 %, reaching a maximum at a concentration of 1.4 M. Particular attention is paid to the study of the nonlinear optical properties of the synthesized nanopowders using the Second Harmonic Generation (SHG) method under laser radiation. High efficiency of second optical harmonic generation was experimentally confirmed. A clear correlation between the phase composition of nanocrystals and the magnitude of the nonlinear optical response was established. The sample with the maximum content of the noncentrosymmetric wurtzite phase (90 %) demonstrated the highest frequency conversion efficiency (output signal 1150 mV), whereas samples with a lower content of this phase showed lower results. The obtained data prove the possibility of targeted control of the functional properties of nanomaterials by optimizing the electrolyte composition, which is important for creating new effective media for nonlinear optics.
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