Warm-white luminescence of Dy3+ and Sm3+ co-doped NaSrPO4 phosphors through energy transfer between Dy3+ and Sm3+ ions

Series of white light-emitting NaSrPO4:Dy3+ phosphors were synthesized via a sol–gel method. Small amounts of Sm3+ ions were co-doped into the phosphors to enhance their luminescence. The effects of Dy3+/Sm3+ co-doping concentrations and synthesis temperature on the phosphors’ structures and luminescence properties were investigated. The results of X-ray diffraction confirmed that the characteristic diffraction peaks of the phosphors were in accord with those of the standard NaSrPO4 structure. Energy dispersive spectroscopy indicated that the NaSrPO4:Dy3+ samples were prepared with stoichiometric ratios of elements. Under ultraviolet light excitation of 348 nm, the NaSrPO4:Dy3+ phosphors emitted a white light which was composed of two emission peaks at 484 nm (blue) and 577 nm (yellow) corresponding to the magnetic dipole transition 4F9/2 → 6H15/2 and electronic dipole transition 4F9/2 → 6H13/2 of Dy3+ ions, respectively. Based on Sm3+ co-doping, a characteristic red emission at 602 nm arose and a warm-white light containing a lower CCT value was obtained. Besides, the luminescence lifetime of Dy3+ decreased while that of Sm3+ increased as dosages of Sm3+ were added, indicating efficient energy transfer from Dy3+ to Sm3+ happened. Therefore, NaSrPO4:Dy3+, Sm3+ phosphors are promising candidates for application in warm-white light-emitting diodes.