The effects of Mg2+/Si4+ substitution on crystal structure, local coordination and photoluminescence of (Gd,Lu)3Al5O12:Ce garnet phosphor

A series of phase-pure [(Gd 0.6 Lu 0.4 ) 1- y Ce y ] 3 [Al 1- z (Mg/Si) z ] 5 O 12 ( y  = 0–0.012, z  = 0–0.15) garnet phosphors were synthesized via gel-combustion, and the effects of Mg 2+ /Si 4+ substitution on characteristics of the garnet host and Ce 3+ luminescence were investigated in detail. The maximum amount of equimolar Mg 2+ /Si 4+ dopants that can be incorporated into the garnet lattice and the optimal Ce 3+ content for luminescence were determined to be around z  = 0.15 and y  = 0.010, respectively. Mg 2+ /Si 4+ codoping was analyzed to narrow bandgap of the host, non-uniformly compress the [CeO 8 ] dodecahedron , enlarge the [Al-O] polyhedrons and meanwhile alter bond angles. Increasing Mg 2+ /Si 4+ content was found to lower the intensity, fluorescence lifetime and thermal stability of Ce 3+ luminescence and meanwhile red-shift the 4f-5d 1 excitation/emission peaks. The results were interpreted by considering band structure and crystal field splitting of the Ce 3+ 5d energy level. The y  = 0.01 and z  = 0.15 phosphor exhibited a broad emission peaked at ∼561 nm under 457 nm excitation, with CIE color coordinates of around (0.449,0.527), a correlated color temperature of ∼3567 K, a fluorescence lifetime of ∼43 ns, and an activation energy for thermal quenching of ∼0.267 eV. Electroluminescence indicated that the phosphors may find potential application in warm-white LEDs excited by blue-LED chips.