Effect of gadolinium doping on the structural, morphological, vibrational, and optical properties of β−Ga2O3: A solid-state combustion approach

Abstract

This study explores the synthesis and comprehensive characterization of gadolinium (Gd)-doped $\beta -{\mathrm{Ga}}_2{O}_3$ nanoparticles, prepared for the first time via the solid-state combustion method, with Gd doping concentrations of 1%, 2%, and 3%. To date, no prior studies have reported the successful synthesis of Gd-doped $\beta -{\mathrm{Ga}}_2{O}_3$ using this method. X-ray diffraction (XRD) analysis confirmed the retention of the monoclinic crystal structure, with ${\mathrm{Gd}}^{3+}$ ion incorporation leading to peak broadening, reduced intensity, and shifts to higher $2\theta$ angles. These changes, validated through Scherrer and Williamson–Hall analyses, are attributed to lattice strain, reduced crystallite size, and structural distortion induced by substituting smaller ${\mathrm{Ga}}^{3+}$ ions ($0.62\text{Å}$) with larger ${\mathrm{Gd}}^{3+}$ ions ($0.93\text{Å}$). Morphological analysis using field emission scanning electron microscopy (FESEM) revealed polydispersed nanoparticles with irregular shapes and a decrease in particle size with increasing Gd concentration. Energy-dispersive spectroscopy (EDS) confirmed the stoichiometric incorporation of Gd ions into the $\beta -{\mathrm{Ga}}_2{O}_3$ lattice. Raman and Fourier-transform infrared (FTIR) spectroscopy showed reduced intensities, peak broadening, and shifts to higher wavenumbers, indicating increased lattice distortion and strain. UV–Vis spectroscopy demonstrated a reduction in the optical bandgap from 4.6 eV for pure $\beta -{\mathrm{Ga}}_2{O}_3$ to 4.11 eV for 1% Gd doping, with minor increases to 4.16 eV and 4.18 eV at 2% and 3% doping, respectively. This narrowing of the bandgap is attributed to the introduction of defect states within the bandgap, facilitating electronic transitions at lower energies. Photoluminescence (PL) spectra revealed broad emission bands in the 400-600 nm range, with deconvolution identifying prominent peaks in the blue and green regions, corresponding to radiative recombination involving defect states such as oxygen vacancies $\left(V_o\right)$ and gallium vacancies $\left(V_{Ga}\right)$. This work highlights the influence of Gd doping on the structural and optical properties of $\beta -{\mathrm{Ga}}_2{O}_3$ and establishes its potential for ultraviolet photodetectors, luminescent devices, and other optoelectronic applications.