Synthesis and luminescence enhancement of CaySr4−x−yAl2O7:xEu2+ phosphors by a novel halide-assisted solid-state reaction method

Eu 2+ doped strontium aluminate phosphors Ca y Sr 4−x−y Al 2 O 7 :xEu 2+ (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1) were synthesized via a novel halide-assisted solid-state reaction method. The phase structure and photoluminescence properties of Ca y Sr 4−x−y Al 2 O 7 :xEu 2+ were characterized via X-ray diffraction (XRD) and fluorescence spectrophotometer. The XRD patterns indicate that the α-Sr 4 Al 2 O 7 phase structure with negligible impurities were produced in the samples of Ca y Sr 4−x−y Al 2 O 7 :xEu 2+ (x ≤ 0.1 and y ≤ 0.1) at 1450 °C. Photoluminescence results show that the Ca y Sr 4−x−y Al 2 O 7 :xEu phosphor with NH 4 I as reductant presents typical intense Eu 2+ red emission bands centered at 610 nm while excited by 450 nm. Accordingly, samples without NH 4 I only exhibit two weak Eu 3+ emission peaks located at 598 and 619 nm, respectively. It can be ascribed to the reduction characteristic of I − ion. Furthermore, by partial replacement of Sr 2+ with Ca 2+ in Sr 4 Al 2 O 7 host, the emission intensity is enhanced up to 260% with emission peak red shifted by 5–10 nm. These results indicate that partial substitution of Sr 2+ by Ca 2+ is an efficient way to increase the proportion of longer wavelength emission and luminescence intensity for Sr 4 Al 2 O 7 :Eu phosphors.