Effect of Gd doping on structural, optical properties, photoluminescence and electrical characteristics of CdS nanoparticles for optoelectronics

Synthesis of pure and 0.1 to 5 wt.% Gd-doped CdS nanoparticles (NPs) was achieved through a modified domestic microwave-assisted route in a short timespan at 700 W power. The formation of hexagonal CdS NPs was verified via X-ray diffraction analysis, and no structural variation was observed except for lattice variation. The size of the crystallites (D), dislocation concentration, and lattice strain were calculated, and the D was in the range of 3–6 nm. Fourier transform-Raman analysis confirmed the presence of 1LO, 2LO, and 3LO modes at 294.76, 590, and 890 cm ⁻¹ , respectively, in all the synthesized nanostructures, with minute variations in their positions due to doping; however, no new mode was observed. The position of the vibration modes was red shifted compared to that of the bulk material, indicating a confinement effect. Scanning electron microscopy (SEM) mapping/energy-dispersive X-ray spectroscopy revealed homogeneous doping of Gd and the presence of all the constituents in the final products. The morphology of the synthesized materials was tested via field-emission SEM, which revealed spherical NPs with small dimensions. Additionally, high-resolution transmission electron microscopy was performed to visualize the shape and size of the prepared 0.1% Gd:CdS NPs. The energy gap was calculated using the Kubelka–Munk theory and found to be in the range of 2.31–2.41 eV. The photoluminescence emission spectra exhibited two green emission peaks at 516 ± 2 nm and 555 ± 2 nm and showed the reduction of defects with Gd doping in terms of intensity quenching. The dielectric constant (ε ^’ ), loss, and alternating-current electrical properties were studied in the high-frequency range. The values of ε ^’ were in the range of 17–27. An enhancement of these values was observed for CdS when it was doped with Gd. The electrical conductivity exhibited frequency power law behavior.