Hydrothermal Synthesis And Properties Of Red Molybdate Phosphors

Recently, increasing interests were focused on the white-light-emitting diodes (WLEDs) due to their lots of advantages, such as environment-friendly, long lifetime, and high-efficiency. Consequently, it is hopeful green illumination light source. The mainstream scheme to obtain WLED is phosphor conversion. However, the current red phosphor used for WLED displays a rather low efficient red emission under near-UV light excitation. In order to solve these problems, it is needed to be solved to explore highly-efficient red phosphors for WLED.In this paper, a series of anion-doped red phosphors including NaEu(MoO₄)_2-xM_y(M=SiO₃^2-,PO₄^3-,ClO₃^-) and Ca_0.64Eu_0.24(MoO₄)_1-xM_y(M=SiO₃^2-,PO₄^3-,SO₄^2-,ClO₃^-) were prepared by hydrothermal approach. According to experiments, the optimum reaction conditions can be determined. When anions with different valences were introduced into matrix materials and replaced for a divalent MoO₄^2- ion, effective charge compensation was necessarily considered. The doping methods applied in this research were in the followings.The MoO₄^2- ions were supposed to be equivalent replaced by SiO₃^2- or SO₄^2- ions in the molar ratio of 1:1. Whereas, MoO₄^2- ions were replaced by 2/3 PO₄^3- or two ClO₃^- anions, respectively.In order to investigate the influence of different hydrothermal duration and doped anions on the characteristics of samples. excitation and emission spectra,SEM,XRD,EDS were utilized. The results prove that all the samples belong to a tetragonal scheelite-structure. The SEM photographs show that the anions doping (except SiO₃^2-) is able to improve the crystallization of phosphors. All of the samples were excited with near-UV 395nm light displayed superior red emission to the commercial red phosphor (Y₂O₂S:Eu). In particular, with the ClO₃^- anion doped, the relative emission intensity reaches more than 7-fold as compared with that of the commercial Y₂O₂S:Eu.The investigation on the anion-doped phosphors of Eu³⁺ activated molybdates was expected to provide the experimental basis to explore efficient red phosphors for application research of WLED.