Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors with ultrabroad excitation band for white light-emitting diodes

Abstract

A series of novel Eu³⁺-activated La₂MoO₆-La₂WO₆ red-emitting phosphors have been successfully prepared by a citrate-assisted sol-gel process. Both photoluminescence excitation and emission spectra suggest that the resultant products have the strong ultrabroad absorption band ranging from 220 to 450 nm. Under the excitation of 379 nm, the characteristic emissions of Eu³⁺ ions corresponding to the ⁵D₀ → ⁷F _J transitions are observed in the doped samples. The optimal doping concentration for Eu³⁺ ions is found to be 12 mol% and the quenching mechanism is attributed to the dipole-dipole interaction. A theoretical calculation based on the Judd-Ofelt theory is carried out to explore the local structure environment around the Eu³⁺ ions. The studied samples exhibit a typical thermal quenching effect with a T_0.5 value of 338 K and the activation energy is determined to be 0.427 eV. A near-ultraviolet (NUV)-based white light-emitting diode (LED) is packaged by integrating a mixture of resultant phosphors, commercial blue-emitting and green-emitting phosphors into an NUV LED chip. The fabricated LED device emits glaring white light with high color rendering index (84.6) and proper correlated color temperature (6492 K). These results demonstrate that the Eu³⁺-activated La₂MoO₆-La₂WO₆ compounds are a promising candidate for indoor lighting as red-emitting phosphors.