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:xDy3+ and Ba1−yCayLa2−xWO7:xDy3+ (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:xDy3+ 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 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+, respectively. The optimal luminescent condition is at x=0.06 (BaLa1.94WO7:0.06Dy3+). The intensity of the emission from the 4F9/2→6H15/2 transition was higher than that from the 4F9/2→6H13/2 hypersensitive (ΔJ=2) transition, revealing that Dy3+ occupied a relatively symmetrical site in BaLa2−xWO7:xDy3+, 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−ySryLa1.94WO7:0.06Dy3+ series is y=0.25. A partial substitution of Ba2+ with Ca2+ in Ba1−yCayLa1.94WO7:0.06Dy3+ could change the (4F9/2→6H13/2)/(4F9/2→6H15/2) 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−yCayLa1.94WO7:0.06Dy3+ 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.