The effects of Ga3+ substitution on local structure and photoluminescence of Tb3Al5O12:Ce garnet phosphor

(Tb_0.985Ce_0.015)₃(Al_1-xGa_x)₅O₁₂ garnet phosphors (x = 0, 0.1, 0.2, 0.3, and 1.0) were prepared by calcining their coprecipitated precursors in air at 1500 °C, followed by reduction in hydrogen at 1200 °C. Rietveld refinement of the XRD results suggested that the Ga dopant predominantly resides at the octahedral Al site of the garnet lattice. Ga doping led to linearly expanded lattice constant, cell volume and theoretical density of the garnet compound and successively lower intensity and longer average fluorescence lifetime of the ~ 570 nm emission of Ce³⁺. Blue shifted emission and 4f(²F_5/2)→5d₁(E_2g) excitation and red shifted 4f(²F_5/2)→5d₂(E_2g) excitation were also observed for the Ce³⁺ activator at a higher Ga content. The phenomena were interpreted by considering the band structure of the host, distortion of the CeO₈ polyhedron, and centroid shift and field splitting of the Ce³⁺ 5d energy levels.