Novel Eu3+-activated Ba2Y5B5O17 red-emitting phosphors for white LEDs: high color purity, high quantum efficiency and excellent thermal stability

Abstract

Eu³⁺-activated Ba₂Y₅B₅O₁₇ (Ba₂Y_5−xEu_xB₅O₁₇; 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, Ba₂Y_5−xEu_xB₅O₁₇ showed red emission peaking at 616 nm which was attributed to the ⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺ ions. Meanwhile, the influences of different concentrations of Eu³⁺ ions on the PL intensity were also discussed. The optimum concentration of Eu³⁺ ions in the Ba₂Y_5−xEu_xB₅O₁₇ 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 Eu³⁺ ions was determined to be 5.64 Å. The asymmetry ratio [(⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁)] of Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba₂Y_5−xEu_xB₅O₁₇ phosphors. In addition, the CIE color coordinates of the Ba₂Y_4.2Eu_0.8B₅O₁₇ 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 Ba₂Y_4.2Eu_0.8B₅O₁₇ 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 Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors could be potential candidates for application in near-UV excited white light emitting diodes.