Controlled synthesis and luminescence properties of rhombic NaLn(MoO4)2 submicrocrystals

Abstract

Tetragonal phase NaLn(MoO₄)₂ (Ln = Yb, Tm, Er, Y, Dy, Gd, Eu, Sm, and Ce) submicrocrystals were successfully synthesized by a hydrothermal method. It was found that higher reaction temperature and larger ionic radius of RE ions are beneficial for the formation of NaLn(MoO₄)₂ submicrocrystals. NaY(MoO₄)₂ was demonstrated to be a good host material for different lanthanide ions. In the up-conversion luminescence spectra of NaY(MoO₄)₂:Yb³⁺/Er³⁺ under 980 nm excitation, the green emissions (²H_11/2/⁴S_3/2 → ⁴I_15/2) were observed and the red emission (⁴F_9/2 → ⁴I_15/2) completely vanished, which could be attributed to the efficient cross-relaxation of ⁴I_11/2 + ²G_7/2 → ⁴F_7/2 + ²H_11/2/⁴S_3/2 between Er³⁺ ions. In the up-conversion luminescence spectra of NaY(MoO₄)₂:Yb³⁺/Tm³⁺, the blue emissions (¹G₄ → ³H₆ and ¹D₂ → ³F₄) were observed and the near-infrared emission (³H₄ → ³H₆) completely vanished, which could be attributed to the inefficient nonradiative relaxation of ³F_2,3 → ³H₄. In addition, the down-conversion luminescence properties of NaY(MoO₄)₂:Eu³⁺ were studied in detail.