Hydrothermal-assisted ion exchange synthesis and photoluminescence of Li+ and Eu3+ co-doped NaLa(WO4)2 as near-UV type red phosphors

A series of Li⁺ and Eu³⁺ co-doped double tungstate NaLa(WO₄)₂ (NLW) red phosphors have been successfully synthesized by an ion exchange method under a hydrothermal condition. The effects of Li⁺ doping concentration on the crystal structure, morphology and photoluminescence properties were investigated using the XRD, TEM and photoluminescence (PL) measurements. The results reveal that the samples have phase-pure scheelite structure and adopt spherical particle morphology. Furthermore, room temperature PL spectrum shows that the optical brightness is highly dependent on the concentration of doping Li⁺, which is determined by ion exchange duration and the precursor concentration of LiNO₃. As 5% Li⁺ ions was introduced into the crystal lattice, the emission intensity was enhanced by more than 10-fold as compared with the pristine one. Moreover, the co-doping of Li⁺ can substantially improve the effective excitation of the NaLa(WO₄)₂:Eu³⁺ phosphors under near-UV region.