Enhancement of luminescence properties via the substitution of Ba2+ by Sr2+ and Ca2+ in the white phosphors Ba1-yMyLa2-xWO7:xDy3+ (M=Sr, Ca) (x=0.01-0.4, y=0-0.4)

Ba1-ySryLa2-xWO7:xDy(3+) and Ba1-yCayLa2-xWO7:xDy(3+) (x=0.01-0.4, y=0-0.4) phosphors were synthesized by a solid-state reaction, and their luminescence properties were investigated. BaLa2-xWO7:xDy(3+) is a near-white-light emitting phosphor. Under ultraviolet (351 nm) excitation, the emission spectra exhibited two groups of strong peaks at 485 and 572 nm due to the F-4(9/2) --> H-6(15/2) and F-4(9/2) --> H-6(13/2) transitions of Dy3+, respectively. The optimal luminescent condition is at x=0.06 (BaLa1.94WO7:0.06Dy(3+)). The intensity of the emission from the F-4(9/2) --> H-6(15/2) transition was higher than that from the F-4(9/2) --> H-6(13/2) hypersensitive (Delta J=2) transition, revealing that Dy3+ occupied a relatively symmetrical site in BaLa2-xWO7:xDy(3+), and that the doping of Dy3+ ions did not change the site symmetry even at a high concentration of x=0.4. Introducing Sr2+ into Ba2+ site could further enhance the emission intensity but did not change the site symmetry around Dy3+. The optimal luminescent condition of the Ba1-ySryLa1.94WO7:0.06Dy(3+) series is y=0.25. A partial substitution of Ba2+ with Ca2+ in Ba1-yCayLa1.94WO7:0.06Dy(3+) could change the (F-4(9/2) --> H-6(13/2))/(F-4(9/2) --> H-6(15/2)) yellow-to-blue ratio from 0.89 to 1.27 when the Ca2+ content was increased from y=0 to y=0.3. The emission color of the Ba1-yCayLa1.94WO7:0.06Dy(3+) phosphors can be tuned by changing the amount of Ca2+ substitution. The CIE coordinates (x, y) varied from (0.323, 0.383) at y=0 to (0.339, 0.358) at y=0.3, corresponding to a near-white color under UV excitation at 351 nm. (C) 2012 Elsevier B.V. All rights reserved.