Tunable luminescence and energy transfer of a Eu2+/Mn2+ co-doped Sr3NaY(PO4)3F phosphor for white LEDs

Abstract

A series of single-phase and color-tunable Sr₃NaY(PO₄)₃F:Eu²⁺, Mn²⁺ phosphors have been successfully prepared via the solid-state reaction. The crystal structure and phase of the prepared phosphors were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The excitation and emission spectra, and fluorescence decays were measured and discussed systematically. The results revealed that Eu²⁺ can efficiently transfer excitation energy to Mn²⁺ via its 4f states and therefore sensitizes Mn²⁺ emission under near-ultraviolet (NUV) excitation. In addition, the energy transfer mechanism was demonstrated to be a resonant type via a dipole–dipole process. The corresponding Commission Internationale deL'Eclairage (CIE) chromaticity coordinates showed that the emission colors of the phosphors can be tuned from blue (0.133, 0.148) to white (0.327, 0.351) by adjusting the ratio of Eu²⁺ and Mn²⁺. Meanwhile, the good thermal stability of Sr₃NaY(PO₄)₃F:0.03Eu²⁺, 0.12Mn²⁺ sample showed that the emission intensity at 150 °C was reduced from 100% to 72.3% measured at 25 °C. The results confirmed that the as-synthesized Sr₃NaY(PO₄)₃F:Eu²⁺, Mn²⁺ phosphors have strong potential to be used as single-phase and NUV excitable white-emitting phosphors.