Synthesis, Structure And Properties Of Rare Earth Tungstates And Molybdates

Rare tungstates and molydateds have received increasing research attentions due to their special physical and chemical properties in a wide range of applications such as visual display, solid-state lighting, scintillators and catalytes. A series of Li+and Eu3+co-doped double tungstate NaLa(WO4)2, LiLn(MO4)2:Eu3+(Ln=La, Eu, Gd, Y, M=W, Mo) and LiLn(MO4)2(Ln=La, Ce, M=W, Mo) have been synthesized. Their optical and electrochemical properties have been investigated in details. The contents can be summaried as follows:1. A simple hydrothermal-assisted ion exchange method has been established to synthesize well-crystallized NaLa(WO4)2:Eu3+,Li+red phosphors having different Li doping concentrations. The effects of Li+doping concentration and ion-exchage duration and the amount of surfactant (PVP) on the crystal structure, morphologies and photoluminescence properties have been investigated in details.The results reveal that the samples have phase-pure scheelite structure. It is clear that the sample is mainly composed of spherical particles and a small amount of dendrite crystals in micrometer scale. Room temperature PL spectrum shows that the as-prepared samples can be effectively excited by a near-UV light of396nm, emitting red light. Moreover, the co-doping of Li+can considerably improve the effective excitation of the NaLa(WO4)2:Eu3+phosphors under near-UV region. The optical brightness is highly dependent on the concentration of doping Li+which is in turn determined by ion exchange duration and the precursor concentration of LiNO3. As5%Li+ions is introduced into the crystal lattice, the emission intensity is enhanced by more than10-fold as compared with the pristine one.2. A facile sol-gel method has been exploited to rationally synthesize LiLa(WO4)2:Eu3+red phosphors and the influences of the calcination temperature, the ratio of citric acid to metal ions (CA/M), as well as pH, on the crystal structure and PL properties have been discussed in details. And the same procedure has also been used to prepare a series of LiLn(MO4)2:Eu3+(Ln=La, Eu, Gd, Y, M=W, Mo) red phosphors. The XRD results indicate that the LiLn(MO4)2:Eu3+(Ln=La, Eu, Gd, Y, M=W, Mo) samples synthesized by sol-gel method are well crystallized with scheelite structure. Irrespective of the type of rare-earth ions, La3+, Eu3+, Gd3+, or Y3+, the as-obtained LiLn(MO4)2samples have single phase structure. The as-prepared LiLn(MO4)2:Eu3+samples can emit bright red light after being excited by a typical near-UV light of396nm. Under an optimized conditions of calcination temperature800℃, the ratio of citric acid to metal ions2.5:1, and the pH value1, the LiLa(WO4)2:Eu3+sample exhibits the relatively strongest PL brightness. With the decreasing of ion radius of rare earth (La3+(1.06A)>Gd3+(0.94A)>Y3+(0.88A)), the PL intensity of LiLn(MO4)2:Eu3+(Ln=La, Gd, Y, M=W, Mo) samples are increasing. It is found that LiEu(MoO4)2displays the strongest emission intensity in the as-obtained samples. In addition, comparing with the double tungstate red phosphors, all the double molybdate red phosphors exhibit more excellent photoluminescence properties.3. LiLn(MO4)2(Ln=La, Ce, M=W, Mo) have been prepared by sol-gel method and the electrochemical performance of these new materials are studied by employing these nanoparticles as new anodes for Li-ion batteries.The results demonstrate that the as-obtained LiLn(MO4)2(Ln=La, Ce, M=W, Mo) samples have phase-pure scheelite structure and show an excellent electrochemical performance. A stable reversible capacity of approximately739.6mAh·g-1is observed in the case of LiCe(Mo04)2at a current density of60mA·g-1, which is better than that of traditional graphite.