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

A series of Sr9Mg1.5(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 Sr9Mg1.5(PO4)(7):0.01 Tm3+, yDy(3+) (0 <= y <= 0.20) turned from blue to white by modifying the Tm3+/ Dy3+ ratio. The overlapped PL/PLE spectra and decreasing lifetimes of Sr9Mg1.5(PO4)(7):Tm3+, yDy(3+) indicated the energy transfer from Tm(3+)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 Sr9Mg1.5(PO4)(7):0.01 Tm3+, 0.20Dy(3+) 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 degrees C compared with the original emission intensity at ambient temperature. The outstanding luminescence properties and excellent thermal stability suggested that Sr9Mg1.5(PO4)(7):0.01 Tm3+, 0.20Dy(3+) phosphor had a potential application in WLEDs.