Synthesis,structural characterization and luminescent properties of Tb3+-doped AgLaP2O7 phosphors

Silver lanthanum diphosphates doped with terbium, AgLa_1-xTb_xP₂O₇ (x=0%, 1%, 5%, 10%, 15% and 20%), were prepared by solid state reaction at T=500°. The obtained compounds were investigated by means of a multi-methodological approach, involving the Scanning Electron Microscopy (SEM) equipped with energy dispersive X-Ray spectroscopy (EDS) for morphological investigation and semi-quantitative chemical analysis, respectively; powder X-ray diffraction (PXRD) for structural characterization and Rietveld refinement; Fourier Transform InfraRed (FTIR) and Raman spectroscopies for qualitative study. Finally, emission spectra were collected in order to detect the fluorescence properties of the compounds.The unit cell parameters and the space group of all the family members were determined by PXRD data. The compounds crystallize in the orthorhombic Pnma space group, with the AgLaP₂O₇ cell constants equal to: a?=?8.6706(1) Å, b?=?5.3218(1) Å, c?=?12.8839(1) Å and cell volume V?=?594.51(1) ų. A decreasing trend for unit cell parameters was observed at increase of dopant concentration. For the pure phase, the investigation was completed with the structure solution via Direct Methods and Rietveld refinement. The crystal structure consists of compact layers of LaO₉ polyhedra, down the c axis, bridged by P₂O₇ diphosphate groups and by zig-zag chains of AgO₉ polyhedra down b.The FTIR and Raman analysis supports the chemical structure, highlighting the deformation (δPO₃) and stretching (νPO₃) vibration of PO₃ groups, and the characteristic bands of P₂O₇^4- groups attributed to the symmetric and asymmetric stretching (ν_s and ν_as) of P-O-P bridge, respectively.The luminescence properties of Tb³⁺ activating ion in AgLa_1-xTb_xP₂O₇ (x=1%, 5%, 10%, 15% and 20%) were also examined. No concentration quenching of the main ⁵D₄-→⁷F₅ emission, responsible for the well known green emission of Tb³⁺ ion, was observed in the studied concentration range, whereas a concentration quenching of the emission from ⁵D₃ level, due to ⁵D₃^-→⁵D₄ cross relaxation process, was revealed.