A novel tunable color emitting phosphor Sr₃YLi(PO₄)₃F:Eu²⁺, Mn²⁺ for near-UV white LEDs based on the energy transfer from Eu²⁺ to Mn²⁺

Novel Eu²⁺ and Mn²⁺ doped fluorapatite-type Sr₃YLi(PO₄)₃F powder materials have been synthesized via high temperature solid state reaction. The samples are characterized by X-ray diffraction (XRD), scanning electric microscopy (SEM), photoluminescence (PL) and photoluminescence excitation (PLE) spectra. Eu²⁺ single doped Sr₃YLi(PO₄)₃F host displays a blue emission ranging from 400 to 550 nm centered at 439 nm, and exhibits a broad excitation band varying from 225 to 425 nm which matches with commercial n-UV LEDs (360–410 nm). Under near-UV light irradiation in the range from 270 to 410 nm, Eu²⁺ and Mn²⁺ co-doped Sr₃YLi(PO₄)₃F phosphors show two emission bands centered at 439 and 565 nm, respectively. The relative intensity ratio of Eu²⁺ and Mn²⁺ can be changed by increasing the amount of Mn²⁺ ions, the emission color can be regulated from blue to white. The energy transfer process from Eu²⁺ to Mn²⁺ has been proved to the resonant type through the quadrupole–quadrupole interaction mechanism. It is important that the white light emission can be gained by modulating the relative contents of Eu²⁺ and Mn²⁺ ions in Sr₃YLi(PO₄)₃F host. Base on the obtained results, the as-prepared phosphors might be applied as a candidate for white LEDs.