Novel Eu(3+)-activated Ba(2)Y(5)B(5)O(17) red-emitting phosphors for white LEDs: high color purity, high quantum efficiency and excellent thermal stability

Eu(3+)-activated Ba(2)Y(5)B(5)O(17) (Ba(2)Y(5−x)Eu(x)B(5)O(17); x = 0.1–1) red-emitting phosphors were synthesized by the conventional high temperature solid-state reaction method in an air atmosphere. Powder X-ray diffraction (XRD) analysis confirmed the pure phase formation of the as-synthesized phosphors. Morphological studies were performed using field emission-scanning electron microscopy (FE-SEM). The photoluminescence spectra, lifetimes, color coordinates and internal quantum efficiency (IQE) as well as the temperature-dependent emission spectra were investigated systematically. Upon 396 nm excitation, Ba(2)Y(5−x)Eu(x)B(5)O(17) showed red emission peaking at 616 nm which was attributed to the (5)D(0) → (7)F(2) electric dipole transition of Eu(3+) ions. Meanwhile, the influences of different concentrations of Eu(3+) ions on the PL intensity were also discussed. The optimum concentration of Eu(3+) ions in the Ba(2)Y(5−x)Eu(x)B(5)O(17) phosphors was found to be x = 0.8. The concentration quenching mechanism was attributed to the dipole–dipole interaction and the critical distance (R(c)) for energy transfer among Eu(3+) ions was determined to be 5.64 Å. The asymmetry ratio [((5)D(0) → (7)F(2))/((5)D(0) → (7)F(1))] of Ba(2)Y(4.2)Eu(0.8)B(5)O(17) phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba(2)Y(5−x)Eu(x)B(5)O(17) phosphors. In addition, the CIE color coordinates of the Ba(2)Y(4.2)Eu(0.8)B(5)O(17) phosphors (x = 0.653, y = 0.345) were found to be very close to the National Television System Committee (NTSC) standard values (x = 0.670, y = 0.330) of red emission and also showed high color purity (∼94.3%). The corresponding internal quantum efficiency of the Ba(2)Y(4.2)Eu(0.8)B(5)O(17) sample was measured to be 47.2%. Furthermore, the as-synthesized phosphors exhibited good thermal stability with an activation energy of 0.282 eV. The above results revealed that the red emitting Ba(2)Y(4.2)Eu(0.8)B(5)O(17) phosphors could be potential candidates for application in near-UV excited white light emitting diodes.