Cations distribution, optical and radiation shielding investigations of ZnAl2O4 doped with different metals: Ni, Mn and Mg

Nanocrystalline ZnAl₂O₄ undoped and doped with different metals (Ni, Mn and Mg) has been prepared applying the solid-state reaction method. Analysis of synchrotron x-ray diffraction patterns revealed the formation of a major phase with a cubic spinel structure, $Fd\bar{3}m$, alongside tiny phases unobservable without synchrotron radiation. Incorporation of the dopant elements into the ZnAl₂O₄ lattice is confirmed by FTIR and Raman spectroscopic analysis. Rietveld structural analysis revealed a partial inverse structure for the pure ZnAl₂O₄ sample with an inversion parameter of 0.146 which increased upon doping with Mg or Ni but reduced upon doping with Mn. UV–Vis diffuse reflectance revealed a significant increase in absorption, especially in the visible region upon doping with Mn or Ni, with a substantial reduction in the optical bandgap from 4.0 eV to 1.62, 1.9 eV respectively. The reduction in the bandgap energies was confirmed by excitation and emission photoluminescence (PL) measurements. The PL intensity was almost totally quenched for samples containing Ni or Mn. The undoped and doped samples displayed violet-blue colors, with different intensities. At 0.015 MeV, the linear (LAC) and mass attenuation coefficient (MAC) values for undoped and doped ZnAl₂O₄ samples with Ni, Mn, or Mg are (127.1, 233.0, 205.7, 169.0 cm⁻¹) and (31.9, 58.1, 50.9, and 43.0 cm²/g), respectively. The half value layers (HVL) and tenth value layers (TVL) values decreased when ZnAl₂O₄ was doped with either Ni, Mn or Mg at both low and high photon energy. ZnAl₂O₄ doped with Ni exhibited the smallest mean free path (MFP) value throughout both lower and higher photon energy ranges. Compared to ZnAl₂O₄, the samples containing doped samples display elevated effective atomic number (Z_eff) values. The impact of doping on the fast neutron removal cross-section (FNRCS), exposure buildup factor (EBF) and energy absorption buildup factor (EABF) parameters was also explored. The quenched intensity of PL emission and the reduction in the bandgap energy, obtained via Ni or Mn doping, signify that the samples are appropriate for photocatalytic applications.