Structural, morphological and photoluminescence properties of Gd_2.97Al_5-xGa_xO₁₂:Ce_0.03 nanophosphors synthesized by a simple sol–gel route

Gd_2.97Al_5-xGa_xO₁₂:Ce_0.03 (x = 0, 1, 2, 3, 4, 5) powder nanophosphors have been successfully synthesized by the sol–gel process and annealed at 1300 °C for 3 h. The influence of Ga content on garnet phase stabilization, secondary phase evolution, size and morphology of particles and luminescent properties of Gd_2.97Al_5-xGa_xO₁₂:Ce_0.03 phosphors were studied and discussed. X-ray diffraction analysis indicated that the stabilization of the garnet cubic structure is strongly influenced by Ga content. When x ≤ 2, the cubic and perovskite phases were formed with different proportions. For x = 3, the desired single cubic phase of garnet is obtained and corresponding Ga content is optimal. However, when x ˃ 3, although Gd₃Ga₁O₆ emerged as a secondary phase, the cubic structure stayed the dominant phase. Field Emission Scanning Electron Microscopy micrographs revealed that all nanophosphors exhibit an interconnected bacteria-like morphology and quasi-identical size of particles. The characteristic emission of Ce³⁺ in garnet structure was observed for x ≤ 3 and high luminescence efficiency was obtained for x = 1. When x ˃ 3, a strong quenching of luminescence was observed. Additionally, increasing Ga content resulted in decreasing crystal field splitting and a blue shift of 5d₂ levels of the excitation spectra and the 5d − 4f luminescence band of the emission spectra, whereas, the 5d₂ levels of the excitation spectra exhibited a red-shift.