Spectroscopic and morphological studies of pure and Eu³⁺ doped silver molybdate obtained by the coprecipitation methodology

Full text: In this work, the crystals of pure and Eu³⁺ β-Ag₂MoO₄ were obtained by coprecipitation method. Initially 1 mmol of the respective precursors AgNO₃ and Na₂MoO₄.2H₂O were dissolved separately in 50 mL of water. A third solution containing Eu³⁺ ions was prepared by opening the Eu₂O₃. Finally, the solutions containing the Ag⁺ and Eu³⁺ ions were mixed and after 10 minutes, this solution was added to the previous solution containing MoO₄ ^-2 ions. The formed powders were then washed with water, separated by centrifugation and oven dried at 60 °C. The materials were characterized using X-ray diffraction (XRD) techniques, scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL). Analysis of the X-ray diffraction patterns showed that both the pure and the doped samples were perfectly monophasic, having a spinel structure with space group Fd-3m, indexed to ICCD card No.08-0473. For the doped samples a small displacement was observed. This displacement can be associated to the distortions caused in the network due to the difference in the electronic density of the Eu³⁺ ion compared to Ag⁺. Through the SEM micrographs it was possible to observe the formation of irregular agglomerates with elongated particles. The Raman spectra presented 5 active vibrational modes, they are: A1_g, E_g, 3T2_g, indicating a structure ordered in the short range. In the PL, the excitation of the samples under air laser at 350nm at room temperature resulted in emission spectra with intense and well defined peaks referring to the characteristic transitions of Eu³⁺. The ⁵D-⁷F₂ transition corresponding to the red color characteristic of this ion was the most intense. The ⁵D-⁷F₂ transition corresponding to the red color characteristic of this ion was the most intense. Reference: [1]. S. K. Gupta, et al. Dalton Trans. v. 44, p 19097-19110, 2015. (author)