Enhanced photoluminescence properties of Gd (x-1) Sr x O: CdO nanocores and their study of optical, structural, and morphological characteristics

Abstract

Synthesis of Gd doped Srx O: CdO (x = 1.4, 1.6, 1.8) nanostructures (NS) was achieved through the coprecipitation method by using CTAB (cetyl trimethyl ammonium bromide) with the purpose to investigate the effect of Gd doping on the optical, structural, morphological, and photoluminescence properties at room temperature. Mixed phase of tetragonal crystal structure verified via X-ray diffraction technique, no structural variation was observed except lattice distortion. Size of the crystallites (D), morphology studied by SEM (scanning electron microscopy) analysis, nanoparticles (NPs) crystalized roughly flake-like morphology with homogeneous particle distribution centered at ~ 78 nm, ~56 nm, ~65 nm, ~88 nm for pure and Gd (x-1) doped Sr xO: CdO nanostructure, respectively. Fourier transform infrared spectroscopic investigation (FTIR) revealed the presence of Gd–O–Gd, Cd–O, Sr–O, and OH peaks appeared at ~1321 cm −1, ~1550 cm −1, ~1400 cm −1–3300 cm −1 with small variation in vibration modes due to Gd doping. Optical absorptivity observed in the range of 325 nm–359 nm (redshifted) with absorption edges at 346 nm, 364 nm, and 380 nm for Gd (x-1) doped Sr xO: CdO nanostructure, respectively. This redshift on the bandgap was discussed in terms of new band levels below conduction band. The energy gap was calculated using Kubelka-Munk theory and was found to be in the range of 3.22 eV–2.61 eV. X-ray photoelectron spectroscopy (XPS) performed to determine chemical composition and binding energies of Gd 3d 3/2, Sr 3d 3/2, and Cd 3d 3/2, O1s, and C1s observed at 150.8 eV, 141.6 eV, 411.0 eV, 530.4 eV, and 285.6 eV indicating Gd+3 ion replaces Sr+2 in all concentrations. Our results showed that Gd-doped Sr xO: CdO nanoparticles exhibited enhanced photoluminescence (PL) properties in contrast to the pure Gd2O3 with Gd+3 randomly incorporated into crystal structure, probably in tetrahedral sites. The composition of Gd 0.6 doped Sr x O: CdO NS exhibited photoluminescent emission spectra, peaks centered at 433 ± 3 nm, 449 ± 3 nm, and 469 ± 2 nm (λ excitation = 318 nm) and for Gd 0.8 doped Sr x O: CdO nanostructure showed broad emission peak at 412 ± 2 nm to 433 ± 2 nm (λ excitation = 380 nm), which indicates a reduction in defects with an increase in Gd doping. The transitions can be ascertained with shielding of 4f shells of Gd +3 ions by 6s, 5d shells by the interaction of other Gd +3 ions.