Multicolor tunable luminescence and energy transfer of Tb3+/Eu3+ doped NaLaP2O7 pyrophosphate phosphors

The pyrophosphate NaLaP2O7 (NLP) samples doped with Tb3+ and Eu3+ were prepared by a simple high-temperature solid state reaction method. The XRD, SEM and spectroscopy were used for characterization. The phosphors exhibited a pure phase identified by XRD. The powders are aggregates of much smaller particles with individual sizes of about 1 μm or even smaller in diameter. The crystal structures were refined by the Rietveld method, and the unit cell parameters decreased with increasing doping concentration. The luminescence properties of the phosphors are analyzed in detail. The optimal doping concentration was determined to be 16 at.% for NLP:Tb3+ and 10 at.% for NLP:Eu3+. The color tunable luminescence from green to red was achieved by co-doping Tb3+ and Eu3+. The fluorescence dynamics fitting based on the Inokuti-Hirayama model revealed that the energy transfer mechanism is mainly contributed by the electronic dipole-dipole interaction. The energy transfer efficiency from Tb3+ to Eu3+ under 376 nm excitation is more than 50 % when the concentration of Eu3+ exceeds 10 %. Under 376 nm excitation, the emission intensity of NLP:0.16 Tb3+, 0.10Eu3+ at 423 K remains 86 % of that at room temperature, and the quantum efficiency of NLP:0.16 Tb3+, 0.10Eu3+ at room temperature is 44.29 %. The results indicate that the prepared NLP:Tb3+, Eu3+ is potential for pc-WLED applications.