Optical and thermal characterization of microcrystalline Na3RE(PO4)2:Yb orthophosphates synthesized by Pechini method (REÂ =Â Y, La, Gd)

Na3RE(PO4)2 orthophosphates (RE = Y, La, Gd) doped with Yb3+ ions were synthesized by Pechini method and characterized by differential scanning calorimetry/thermogravimetric analysis, X-ray diffraction, IR and Raman spectroscopies as well as optical techniques (emission spectra and fluorescence decay time). All measurements, apart from DSC, were performed at room temperature. The spectroscopic properties were discussed in terms of the structure of the obtained materials. They show that lanthanum and gadolinium phosphates synthesized by Pechini method crystallize in the orthorhombic structure, similar to that of Na3Ce(PO4)2. For the first time double sodium yttrium orthophosphate has been obtained in monoclinic modification, that could be compared to one of the Na3Gd(PO4)2 polymorph. Annealing of the obtained orthophosphates at 700 °C leads to grain of ∼200 nm. The microstructure of the powders annealed at 700 °C strongly depends on RE3+ cations.