Study on Luminescence Properties of Bi3+, Eu3+ Co-doped Tb3+:Gd3Al5O12 Phosphors

Abstract

Eu^(3+), Bi^(3+) co-doped Gd₃Al_(5)O_(12):Tb^(3+) phosphors were synthesized by means of solvothermal reaction method. Structural and luminescent properties of these phosphors were investigated by XRD, SEM, PL and decay curves measurements. All phosphors were confirmed their garnet structure with cubic phase. The particles show spherical morphology within the range from nanometer to micrometer. For the Gd₃Al_(5)O_(12):Tb^(3+) phosphors, the excitation spectra consist of three broad bands due to 4f^(8)→4f^(7)5d¹ transitions and some sharp peaks due to 4f^(8)→4f^(8) transitions. Emission spectra of these phosphors reveal mainly two colors, such as blue due to (^(5)D₃→^(7)F_(5)) transition and green due to (^(5)D₄→^(7)F_(5)) transition. When the concentration of Tb^(3+) was 0.5 mol%, the cross-relaxation begins and the green emission intensity continuously increased to 5 mol%. when the Tb^(3+) concentration increases above 5 mol% the intensity began to decrease due to concentration quenching. For the Bi^(3+) co-doped Gd₃Al_(5)O_(12):Tb^(3+) phosphors, the strong excitation band peaked at 286 nm overlapping with 4f^(8)→4f^(7)5d¹ transition of Tb^(3+) and ¹S_(0)→³P₁ transition of Bi^(3+). The green emission of Tb^(3+) was increased by doping Bi^(3+) ions and reached a maximum at 0.5 mol% concentration of Bi^(3+). The intensity of Bi^(3+) co-doped GAG:Tb^(3+)_(0.07), Bi^(3+)_(0.005) phosphors was increased by a factor of 1.9 in comparison with that of GAG:Tb^(3+)0.07 phosphors. This means that the excitation energy absorbed by Bi^(3+) ions was not only transferred to Tb^(3+) ions, but Bi^(3+) ions also play a role as sensitizer. For the Eu^(3+) and Bi^(3+) co-doped Gd₃Al_(5)O_(12):Tb^(3+) phosphors, the emission spectra show strong green and red emissions in between 480 nm and 650 nm. With increasing Eu^(3+) concentration, the emission intensity of Tb^(3+) decreases and also Eu^(3+) emission increases through the energy transfer from Tb^(3+) to Eu^(3+) ions. So, we could suggest that the Bi^(3+) doped GAG:Tb^(3+) phosphors are promising materials in green region for optical display system applications and the Eu^(3+) and Bi^(3+) co-doped Gd₃Al_(5)O_(12):Tb^(3+) phosphors show a hint at the promising application to produce white light through the color tuning.