Abstract
In this study, Pechini method was used to synthesise ZnAl2O4 phosphors doped with Fe3+ to investigate the effects of Fe3+ dopant concentration on the magnetic and photoluminescent properties of these phosphors. X-ray diffraction (XRD) was used to study the crystal structure of the synthesised phosphors and subsequently calculate the crystallite sizes and strains induced in the crystal lattice upon Fe3+ ions doping. Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to determine the morphology and elemental composition of the phosphors, respectively. The magnetic properties of the synthesised materials were investigated using vibrating sample magnetometer (VSM) while photoluminescence (PL) spectroscopy was used to study the luminescence properties of these materials. The XRD results revealed that Fe3+ doping did not alter the crystal structure of the host material since no extra secondary peaks were observed. Morphological studies revealed that the phosphors were composed of irregular shaped particles with higher Fe3+ doping resulting in the phosphors having flat-like structures. Photoluminescence study of the phosphors exhibited peaks at 407 and 430 nm for the undoped sample which were quenched by the introduction of Fe3+ ions. Fe3+ doped samples exhibited emission peaks at 417, 440, and 745 nm with 0.05 mol% doping producing the most intense emission peaks above which the PL emission intensity dropped due to concentration quenching effects. The 417 and 440 nm peaks belong to the tetrahedrally coordinated Fe3+ ions while the 745 nm peak was accountable to octahedrally coordinated Fe3+ ions. The calculated CIE (Commission Internationale de I’Eclairage) confirmed that pure ZnAl2O4 colour emission was lying in the blue region and upon Fe3+ doping the colour coordinates shifted closer to white region for 0.01 and 0.025 mol% doping, above which the colour emission lied in the blue region. VSM measurements showed diamagnetic behaviour for the ZnAl2O4 host lattice. The Fe3+ dopant concentration used in this study seemed to be too low to facilitate transition from diamagnetic behaviour. However, 0.08 mol% Fe3+ doped samples showed enhanced magnetism yielding to the calculated effective magnetic moment close to the theoretical value of 5.92 𝜇𝐵. The obtained results in this study show that ZnAl2O4: Fe3+ is promising phosphor for white LED (light emitting diode) technology.
Magnetic and photoluminescent properties of ZnAl2O4 doped with Fe3+.