Enhanced Green Luminescence of La_9.33Si₆O₂₆:Tb³⁺ Phosphors

This study focuses on the synthesis and characterization of La_9.33Si₆O₂₆:Tb³⁺ phosphor produced through the sol–gel method. The structural analysis conducted using x-ray diffraction confirmed a hexagonal apatite crystal structure with the P63/m space group. The functional groups were analyzed using Fourier-transform infrared spectroscopy. Scanning electron microscopy images displayed uniform spherical particles. Photoluminescence (PL) studies revealed strong excitation and emission properties, with distinct peaks corresponding to the spin-allowed and spin-forbidden transitions of Tb³⁺ ion. The PL excitation spectra, measured at an emission wavelength (λ_em) of 543 nm, exhibited a significant peak at 230 nm attributed to the 4f–5d spin-allowed transition of Tb³⁺ ions, splitting into a band at 274 nm due to spin-forbidden 4f–4f transitions. The emission spectra, excited (λ_exc) at 274 nm, displayed multiple peaks in the blue region at 420 nm, 438 nm, 452 nm, and 470 nm, corresponding to the ⁵D₃ → ⁷F₅, ⁵D₃ → ⁷F₄, ⁵D₃ → ⁷F₃, and ⁵D₃ → ⁷F₂ transitions, respectively. Additionally, peaks in the 480- to 650-nm segment indicated different transitions, showing the efficiency of the host lattice. The prominent emission peaks at 490 nm (⁵D₄ → ⁷F₆), 543 nm (⁵D₄ → ⁷F₅), 585 nm (⁵D₄ → ⁷F₄), and 622 nm (⁵D₄ → ⁷F₃) are due to the transition of Tb³⁺ ion. The peak at 543 nm, corresponding to the ⁵D₄ → ⁷F₅ transition, is particularly intense, resulting in a bright green luminescence visible to the naked eye under UV excitation. Vacuum PL measurements confirmed the green emission characteristics of the synthesized La_9.33Si₆O₂₆:xTb³⁺ phosphors, indicating stable and intense green luminescence. These properties make them ideal for applications that need these characteristics.