Investigation of Structural, Optical, and Emission Properties of Gd³⁺ Doped LiMgBO3 Phosphors Synthesized by Combustion Process

In the present study, lithium magnesium borate doped with different concentrations of gadolinium (LiMgBO3:Gd3+) is synthesized via the combustion route. The prepared phosphors' crystallographic structural, molecular, and micro-morphological changes were tracked using X-ray diffraction, Fourier transform infrared, and field emission scanning electron microscope techniques, respectively. However, the variation of Gd3+ concentration remarkably impacted the crystallite/particle size and lattice strain developed in the host lattice, with 0.50 mol.% achieved the lowest size (28 nm crystallite size and 0.45 µm particle size), molecularly, there were no significant changes. Besides, the spectroscopic absorption features of the synthesized phosphors were analyzed based on the measured diffuse reflectance spectra in the UV-vis-NIR region. The analysis of the direct band gap and Urbach energy using the Kubelka-Munk relation pointed toward a concentration of 0.50 mol.% as an optimized concentration of 5.53 eV and 319 meV. The perturbation subjected to the electronic structure of the LiMgBO3 host by Gd3+ is followed in terms of the calculated energetic positions of the valance and conduction bands. Finally, the photoluminescence characteristics of the prepared phosphors were investigated, which displayed intense multiple UV emission peaks under the excitation of 273 nm light. High controllability of the spectral range of the prepared phosphors’ emission by varying the concentration of Gd3+ and by deducing the optimum concentration for the highest emission intensity, the quenching mechanism was determined.