Synthesis and photoluminescence properties of Eu²⁺-activated Sr₉In_1−yLu_y(PO₄)₇ phosphors

In this work, two series of phosphors of Sr_9−xIn(PO₄)₇:xEu²⁺ and Sr_8.97In_1−yLu_y(PO₄)₇:0.03Eu²⁺ with β-Ca₃(PO₄)₂-type structure are prepared via a high temperature solid-state reaction. The XRD, photoluminescence, photoluminescence excitation spectra and decay times are investigated in detail. Upon excitation at 365 nm, the Sr_9−xIn(PO₄)₇:xEu²⁺ phosphors show a obvious band centered at 410 nm and a little hump peaked at 630 nm ascribed to the 4f⁶5d¹–4f⁷ transitions of Eu²⁺ in different crystallographic sites. The excitation spectra show a broad band in the 250–500 nm, which is well-matched with the NUV LED chip. For the Sr_8.97In_1−yLu_y(PO₄)₇:0.03Eu²⁺ phosphors, the another emission band centered at 520 nm emerged with the substitution of Lu³⁺ for In³⁺ on the basis of Sr₉In(PO₄)₇:Eu²⁺ phosphor under the 365 nm excitation, which indicates that the presence of different Eu²⁺ luminescence centers. And emitting-color can be tuned from bluish-violet to white and yellow-green by varying the ratio of Lu³⁺ and In³⁺. Our results indicate these phosphors can be as an attractive candidate for the application of white LEDs by ions substitution to obtain white light and tunable luminescent.