Monitoring the solvation process and stability of Eu2+ in an ionic liquid by in situ luminescence analysis

Abstract

Abstract Ionic liquids (ILs) offer the remarkable possibility of the direct synthesis of Eu2+-doped nanophosphors in solution, under atmospheric conditions, without the necessity of a high-temperature post-synthetic reduction from its trivalent oxidation state. This work uses for the first time in situ luminescence measurements for monitoring the solvation process of Eu2+ from the solid salt to the IL and its stability against oxidation under atmospheric conditions. Upon the addition of EuBr2 to 1-butyl-3-methyl-imidazolium tetrafluoroborate, the formation of the solvation shell is detected by the shift of the emission band at approximately 24 100 cm−1 assigned to the 5d→4f electronic transitions of Eu2+ within EuBr2 to approximately 22 000 cm−1, assigned to Eu2+ within BminBF4, tracking the time-dependent influence of the Eu2+ coordination environment on the crystal field splitting of its d orbitals. Even though the solubility of EuBr2 was demonstrated to be improved by reducing the concentration and increasing the temperature to 60°C, the performance of reactions at room temperature is recommended for future synthesis of Eu2+ materials in ILs due to the slight oxidation to Eu3+ observed upon heating.