Electronic Raman and fluorescence spectroscopic studies of Eu3+‐doped A2SO4 · χH2O sulphates

Abstract

AbstractIR, Raman (100–6000 cm−1), visible absorption and fluorescence spectra of Eu2(SO4)3 · 8H2O and that doped in A2SO4 · χH2O (with A = Li, Na, K, Rb or Cs) have been studied. The bands observed are analysed in terms of the internal and external vibration modes due to the SO and H2O groups and the Eu3+ electronic Raman transitions. Particular attention is given to the electronic Raman transitions for all the 7F0 → 7FJ′ (J′=1–6) levels in an Eu3+ (4f6) configuration. In this regard, several spectra at different temperatures (77–500 K for solids and 77–360 K for solutions) and concentrations (for solutions) were measured with different lines of an Ar+ laser. This automatically isolates and thus helps in the identification of the bands with different vibrational/electronic Raman, fluorescence or vibronic origins. The bands of H2O are also confirmed by deuteriation. The electronic Raman bands are too weak and in general are masked in the fluorescence. Addition of a few drops of KI in an aqueous solution has been found to depress the intensity for the fluorescence and as a result it facilitates the observation of the electronic Raman effect. The transition energies as observed for the various 7F0 → 7FJ′ Raman bands are consistent with those deduced by the 5D0.1 → 7FJ′ fluorescence and 7F0 → 7FJ′ IR absorptions. The transitions in the Raman and fluorescence processes seem to be inter‐related. The specimens containing the alkali metal cations or the deuteriated salts reveal very intense fluorescence, and only a few and weak Raman bands. The interstate coupling and vibronic decay of the Eu3+ ions through the several radiative and non‐radiative processes operative are generally responsible for these features.