Luminescent properties and energy transfer of double-emitting NaSrPO4:Eu2+,Tb3+ phosphor for near-UV white LEDs

Novel blue/green NaSrPO4 phosphors co-doped with Eu2+ and Tb3+ were synthesized by a conventional solid-state reaction. Their luminescent properties were characterized by using powder X-ray diffraction, photoluminescence excitation and emission spectra, lifetime, and temperature dependent emission spectra, respectively. The NaSrPO4:Eu2+,Tb3+,Na+ phosphor showed an intense broad excitation band between 250 and 430 nm, which was in agreement with the near-UV chip (350–420 nm), and it exhibited two dominating emission bands at 445 and 545 nm, corresponding to the allowed 4f65d1→4f7(8S7/2) transition of Eu2+ ion and the 5D4→7F5 transition of Tb3+ ion, respectively. The emission intensity and lifetime of Eu2+ ion decreased with the increasing concentration of Tb3+ ion, which strongly indicated that an effective energy transfer occurred from Eu2+ to Tb3+ in NaSrPO4 host. The principle of the energy transfer should be the combined effect of the non-radiative resonant energy transfer and the phonon-assisted non-radiative process.