Efficient red phosphors Na₅Ln(MoO₄)₄:EE^u3+ (Ln = La, Gd and Y) for white LEDs

A class of red-emitting phosphors Na₅Ln(MoO₄) ₄ : Eu³⁺(Ln = La, Gd and Y) have been synthesized by the sol-gel technique and their luminescent properties have also been investigated under the near-ultraviolet (n-UV) light. The excitation spectra of these phosphors show the strongest absorption at about 395 nm which matches well with the commercially available n-UV-emitting GaN-based LED chip. Their emission spectra show intense red emission at 618 nm due to the ⁵D ₀-⁷F₂ transition of Eu³⁺. The phosphor Na₅Y_1-xEu_x(MoO₄) ₄ shows the brightest red light among phosphors Na₅Ln _1-xEu_x(MoO₄)₄ as the content of Eu³⁺ is fixed. In addition, the conditions for synthesis of these phosphors are also optimized, including annealing temperature and concentration of Eu³⁺ ions. While the Li⁺ or K⁺ ions are incorporated into Na₅Eu(MoO₄)₄ to substitute for Na⁺ partially, effects on the luminescent properties and structures of phosphors have also been discussed in detail.