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 D-5(0) -> F-7(2) transition. The intensity of the D-5(0) -> (7)F(2 )transition increased with respect to Eu3+ ions concentration in Na2Y2(1-x)B2O7:xEu(3+) (0.05 <= x <= 0.5) phosphors and the luminescence quenching was observed at x = 0.35. The critical distance (R-c) and theta were calculated to be 9.20 angstrom and 5.07, respectively, and thus the dipole-dipole interaction could play a significant role in concentration quenching. The lifetimes of the Na2Y2(1-x)B2O7:xEu(3+) phosphors were calculated for various concentrations (x) of Eu3+ ions. In addition, the determined color purity of Na2Y2B2O7 :0.35Eu(3+) 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 Na2Y2B2O7:0.35Eu(3+) phosphor was 0.16 eV. The above results strongly recommended that the Eu s +/- ions activated Na2Y2B2O7 phosphors can be utilized for solid-state lighting technology such as phosphor converted white-light emitting diodes.