General synthesis of LiLn(MO4)2:Eu3+ (Ln = La, Eu, Gd, Y; M = W, Mo) nanophosphors for near UV-type LEDs

Abstract

A series of Eu³⁺-doped double tungstate and molybdate red phosphors, LiLn(MO₄)₂:Eu³⁺ (Ln = La, Eu, Gd, Y; M = W, Mo), have been successfully synthesized by a simple Pechini method. The procedure involves formation of homogeneous, and transparent, metal–citrate gel precursors using citric acid as a chelating ligand to form metal complexes and ethylene glycol as a cross-linker for polyesterification with the complexes, followed by calcination to promote thermal decomposition of the gel precursors to yield the final LiLn(MO₄)₂ nanoparticles. The as-synthesized nanoparticles were characterized by thermogravimetric/differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) as well as kinetic decay. The results indicate that the obtained LiLn(MO₄)₂:Eu³⁺ samples crystallize in the isostructure with tetragonal space group I4₁/a (no. 88). A room temperature PL spectrum shows that Eu³⁺-doped LiLn(MO₄)₂ powders exhibit an excellent luminescent properties under a near ultraviolet excitation wavelength of 395 nm, suitable for near UV type LEDs. By comparing with other counterparts, it is found that LiEu(WO₄)₂ and LiEu(MoO₄)₂ display the highest emission intensity. In addition, the phosphor of composition LiY_0.95Eu_0.05(WO₄)₂ shows promising application for white light emission with a decay time of 0.585 ms.