Efficient and tunable emission of Na5Lu(WO4)4:Tb3+,Eu3+ phosphors for warm white LEDs with high color rendering index

Abstract

Phosphors with high luminescence efficiency, tunable emission and high color rendering index (CRI) are vital importance for the quality of white light emitting diodes (w-LEDs) in real application. In this work, a new single phase color-tunable Na5Lu(WO4)4:Tb3+,Eu3+ phosphor with outstanding luminescent properties was designed and synthesized. Its crystal structure, electronic structure, and luminescence features were studied in detail. The band gap of the host was calculated to be at about 4.68 eV. The differential charge distribution after Tb, Eu doping through density functional theory simulation theoretically proved the electron redistribution in the W-O bond upon substitution of Tb3+/Eu3+. The energy transfer of Tb3+→Eu3+ enabled tunable emission of luminescent colors from green to orange-red due to the quadrupole-quadrupole interaction. The optimal Na5Lu(WO4)4:60%Tb3+,20%Eu3+ phosphor exhibited excellent photoluminescence quantum yield of 84.19% and good luminescent thermal stability (I423K/298K = 75.90%) with an activation energy of 0.1976 eV. Finally, a white LED device with color coordinates of (0.3371, 0.3636), color rendering index of 89.4 and correlated color temperature of 5334 K was fabricated. These findings demonstrated that Na5Lu(WO4)4:60%Tb3+,20%Eu3+ phosphor could be a potential orange-red-emitting color converter for white LEDs. This work not only assisted in the understanding of experimental observations but also provided a theoretical basis for the rational design of phosphors.