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.