Hydrothermal Synthesis Of Rare Earth Ions Doped Tungstates And Molybdates Solid Solution Microcrystallines And Their Luminescent Properties

Scheelite-type tungstates and molybdates belong to tetragonal symmetry withtetragonal structure,which are the typical self-activated luminescent materials, haveexcellent luminescence properties, and can be extensively applied in the fields such as laserhost material, scintillator medium, solid-state photoconducting device, oxide ion conductorand microwave device and so on. When doped with rare earth ions, tungstates andmolybdates can form a new solid solution with the doped ions, therefore, the new phosphormicrocrystallines can be obtained and their luminescent properties also can be modified.In this article, by using Na₂WO₄, Na₂MoO₄, Eu₂O₃, Sm₂O₃as raw materials,NaRe（MoO₄）_2-x（WO₄）_x（Re=Eu, Sm）, Na_4-3xRe_x（AO₄）₂（Re=Eu, Sm, A=W, Mo） andNa_4-3xRe_x（WO₄）_2-y（MoO₄）y（Re=Eu, Sm） solid solution microcrystallines were synthesizedby hydrothermal method. The crystal structure, surface morphology and room temperaturephotoluminescence properties of the as-synthesized microcrystallines were investigated bythrough X-ray diffraction（XRD）, scanning electron micrograph（SEM） and fluorescenceanalysis（FL）, respectively. The main conclusions acquired from the present work asfollows:（1）A series of NaRe（MoO₄）_2-x（WO₄）_x（Re=Eu, Sm） solid solution microcrystallines havebeen synthesized, the influence of the ratio of WO₄^2-to MoO₄^2-（i.e.x） on the crystalstructure, surface morphology and room temperature photo luminescence properties havebeen discussed in detail. Our results reveal that:â‘ All the obtained NaRe（MoO₄）_2-x（WO₄）_x（Re=Eu, Sm） microcrystallines are wellcrystalized, and they possess single-phase scheelite structure with tetragonal symmetry.â‘¡With the increase of x, the morphology of NaEu（MoO₄）_2-x（WO₄）_xmicrocrystallineschanges from rice-like to sheet-like, and the grain size increases gradually. When thevariation of x is from0.50to1.50, NaSm（MoO₄）_2-x（WO₄）_xmicrocrystallines are spindle-like, and the grain size of the microcrystallines is about1μm-2μm.â‘¢NaEu（MoO₄）_2-x（WO₄）_xseries of phosphors have a strong and broad band from240nm to350nm with a maximum at around280nm,which is attributied Oâ†'Mocharge-transfer transition, and the sharp lines from350nm to575nm belong to f-ftransitions of Eu3+in the host lattices. With the increases of x, the emission peak changesfrom386nm to372nm excited by ultraviolet light. So the emission peak of themicrocrystallines can be adjusted. In addition, the intrinsic emission of Eu3+at592nm（5D0â†'7F1） and614nm（5D0â†'7F2） both appeare obviously, and the emission intensityincreases with the increasing of x, given the maximum at x=1.0. WhenNaSm（MoO₄）_2-x（WO₄）_xphosphors excited with450nm light, the intrinsic emission of Sm³⁺at568nm appears obviously, given the maximum at x=0.5.（2） A series Na_4-3xRe_x（AO₄）₂（Re=Eu, Sm，A=W, Mo） solid solution microcrystallineshave been synthesized, the influence of the ratio of rare earth ions to alkali metal ions（i.e.x）on the crystal properties have been discussed in detail. Our results reveal that:â‘ All the obtained Na_4-3xRe_x（AO₄）₂（Re=Eu, Sm，A=W, Mo） microcrystallines are wellcrystalizd, and they possess single-phase scheelite structure with tetragonal symmetry.â‘¡With the increase of x, the morphology of Na_4-3xEu_x（MoO₄）₂microcrystallineschanges from sheet-like to rice-like, size between about0.2μm⁰.5μm. When x=0.2and0.4, the Na_4-3xEu_x（WO₄）₂solid solution microcrystallines show a spindle shape, and thesamples which x=0.6,1.0and1.2show a mixed shape of spindle and a little spherical grain,in addition, when x=0.8and x=4/3, the crystals show a sheet shape. With increasing x, themorphology of Na_4-3xSm_x（MoO₄）₂microcrystallines changes from round pie-like tospindle-like, and the grain size increases gradually.â‘¢The intrinsic emission of rare earth ions all appeare obviously, and the strength ofemission peak can be controlled by changing the rare earth ions doping amount.（3）A series of Na_4-3xRe_x（WO₄）_2-y（MoO₄）y（Re=Eu, Sm） solid solution microcrystallineshave been synthesized, the influence of the ratio of WO₄^2-to MoO₄^2-（i.e.y） and rare earthions to alkali metal ions（i.e.x） on the crystal structure, room temperature photoluminescence properties have been discussed in detail. The results indicate that:â‘ All the obtained microcrystallines are well crystallized, and they possesssingle-phase scheelite structure with tetragonal symmetry.â‘¡When the variation of x is from0.2to1.0, the morphology ofNa_4-3xEu_x（WO₄）_2-y（MoO₄）ysolid solution microcrystallines changes from spherical-like tospindle-like, and the grain size of them is about2μm. When x=1.2and4/3, the crystals show a sheet shape, and the particle size decreases obviously. When the variation of x isbelow1.2, the morphotogy of Na_4-3x)Sm_x（WO₄）_2-y（MoO₄）ysolid solution microcrystallineschanges from round-like to spindle-like, and the grain size increases gradually withincreasing x.â‘¢The intrinsic emission of rare earth ions all appeare obviously, and the strength ofemission peak can be controlled by changing the rare earth ions doping amount.