Color-tunable luminescence and energy transfer properties of Dy3+/Tm3+ co-doped Sr9Mg1.5(PO4)7 phosphor for light-emitting diodes

A series of Sr₉Mg_1.5(PO₄)₇:Tm³⁺, Dy³⁺ phosphors were prepared by conventional sintering method. Rietveld refinement, X-ray diffraction patterns, PL/PLE spectra, lifetimes and thermal quenching spectra were measured and investigated in detail. All the prepared phosphors crystalized to single phase and consisted of micronized particles. When excited by 358 nm, the emission hue of Sr₉Mg_1.5(PO₄)₇:0.01 Tm³⁺, yDy³⁺ (0 ≤ y ≤ 0.20) turned from blue to white by modifying the Tm³⁺/Dy³⁺ ratio. The overlapped PL/PLE spectra and decreasing lifetimes of Sr₉Mg_1.5(PO₄)₇:Tm³⁺, yDy³⁺ indicated the energy transfer from Tm³⁺ to Dy³⁺. Moreover, the resonance type energy transfer from sensitizer (Tm³⁺) to activator (Dy³⁺), CIE chromaticity and energy transfer efficiency were confirmed and discussed, too. The energy transfer mechanism was determined as a resonant type via dipole-dipole mechanism with 53.05% energy transfer efficiency when the doping content y = 0.02. The CIE chromaticity coordinates of Sr₉Mg_1.5(PO₄)₇:0.01 Tm³⁺, 0.20Dy³⁺ was (0.3279, 0.3299) with 27.8% quantum efficiency. The sample also exhibited excellent thermal quenching performance with the remained 95% emission intensity at 150 °C compared with the original emission intensity at ambient temperature. The outstanding luminescence properties and excellent thermal stability suggested that Sr₉Mg_1.5(PO₄)₇:0.01 Tm³⁺, 0.20Dy³⁺ phosphor had a potential application in WLEDs.