Synthesis, luminescence properties and thermal stability of Eu³⁺-activated Na₂Y₂B₂O₇ red phosphors excited by near-UV light for pc-WLEDs

In the present work, trivalent europium (Eu³⁺) ion activated Na₂Y₂B₂O₇ red phosphors have been synthesized through high-temperature solid-state reaction. X-ray diffraction confirmed the successful formation of Na₂Y₂B₂O₇:Eu³⁺ phosphors with monoclinic phase. Under near-UV light (395 nm) excitation, Na₂Y₂B₂O₇:Eu³⁺ phosphors exhibited red emission around 619 nm due to the ⁵D₀→⁷F₂ transition. The intensity of the ⁵D₀→⁷F₂ transition increased with respect to Eu³⁺ ions concentration in Na₂Y_2(1-x)B₂O₇:xEu³⁺ (0.05 ≤ x ≤ 0.5) phosphors and the luminescence quenching was observed at x = 0.35. The critical distance (R_c) and θ were calculated to be 9.20 Å and 5.07, respectively, and thus the dipole-dipole interaction could play a significant role in concentration quenching. The lifetimes of the Na₂Y_2(1-x)B₂O₇:xEu³⁺ phosphors were calculated for various concentrations (x) of Eu³⁺ ions. In addition, the determined color purity of Na₂Y₂B₂O₇:0.35Eu³⁺ phosphor was 98.2% and internal quantum efficiency was 36.6%. Temperature-dependent photoluminescence study showed that emission intensity at 423 K was 40.2% of its initial at room temperature. The calculated activation energy of the Na₂Y₂B₂O₇:0.35Eu³⁺ phosphor was 0.16 eV. The above results strongly recommended that the Eu³⁺ ions activated Na₂Y₂B₂O₇ phosphors can be utilized for solid-state lighting technology such as phosphor converted white-light emitting diodes.