Preparation And Photoluminescence Of Eu³⁺ Or Tb³⁺ Ions Doped NaLa（MoO₄）₂Phosphors By Microwave-assisted Sol-gel Method

NaLa(MoO4)2, which belongs to double molybdates, are regarded as a type of excellentmatrix materials due to their high physical and chemical stability. In this paper, a newpreparation method, i.e., microwave-assisted sol-gel method for rare earth dopedNaLa(MoO4)2phosphors was explored. It provides many advantages, such as energy savingand high efficiency. A series of Eu3+or Tb3+Ions doped NaLa(MoO4)2phosphors have beensuccessfully synthesized by microwave-assisted sol-gel method. The as-synthesized sampleswere characterized by means of TG-DTA, FT-IR, XRD, SEM and Fluorescencespectrophotometer respectively. The main research contents and results are as follows:(1) The red-emitting phosphors NaLa(MoO4)2:Eu3+was synthesized bymicrowave-assisted sol-gel method. The target products NaLa(MoO4)2:Eu3+have beensynthesized by calcining precursor at700℃to900℃. The obtained products are of purescheelite type molybdate with tetragonal crystal structure. The particles of NaLa(MoO4)2:Eu3+are spherical in shape with a diameter of1~2μm. The excitation spectrum ofNaLa(MoO4)2:Eu3+has a broad band in the range of250~350nm, and the main peak is at301nm. The broad band can be ascribed to the charge transfer band of Mo-O and Eu-O. The sharplines in350~500nm range are due to4f-4f transitions of Eu3+. The emission spectrumcontains a series of narrow peaks, with the main peak at616nm originated from the electricdipole transition of5D0â†'7F2of Eu3+. The phase structure and luminescence properties ofas-synthesized samples were compared with samples prepared by conventional solid-statereaction. Meanwhile, the influences of reaction temperature and time, and flux on thefluorescent properties of as-prepared samples were also investigated.(2) The effects of fluxing agent (H3BO3, NH4F) and co-doping ions (Bi3+, PO43-) on thephase structure and luminescent properties of the red-emitting phosphors NaLa(MoO4)2:Eu3+synthesized by microwave-assisted sol-gel method were investigated. The doping of fluxingagent and co-doping ions have little effect on the crystal structure of the host NaLa(MoO4)2,and it still keeps the tetragonal scheelite-structure. The luminescent intensity ofNaLa(MoO4)2:Eu3+can be enhanced effectively by doping proper amount of H3BO3or NH4F. When the doped concentration of H3BO3or NH4F was3wt%respectively, the luminescentintensity of the samples reaches maximum and the intensity was enhanced about30%or40%,respectively. Doping proper amount of Bi3+or PO43-could increase the emission intensity ofthe samples, the optimum doped amount are2mol%, the intensity of the emission peak at616nm were enhanced about40%or30%, respectively. Moreover, Li+was doped as the chargecompensator, and improved the luminescent intensity of NaLa0.95Eu0.05(MoO4)2-x(PO4)xsamples.(3) A series of green-emitting phosphors NaLa1-x(MoO4)2:Tb3+xwere prepared bymicrowave-assisted sol-gel method. NaLa(MoO4)2:Tb3+phosphors possess the similartetragonal crystal structure as that of NaLa(MoO4)2. The excitation spectrum ofNaLa(MoO4)2:Tb3+is a broad band between250nm and350nm, and the main peak is at300nm. The emission spectrum is composed of a series of sharp lines. The main emission peak isat544nm, which is ascribed to the transition of5D4–7F5. The luminescent intensity ofNaLa(MoO4)2:Tb3+increases with the increase of Tb3+content, and reaches the maximumwhen the content of Tb3+is10mol%, and then decreases with the further increase of Tb3+content. The concentration quenching is caused by the interaction of electric dipole-electricdipole of Tb3+according to the Dexter theory. Moreover, the luminescent intensity ofNaLa(MoO4)2:Tb3+can be greatly enhanced with incorporation of SO42-and SiO44-.