Raman and infrared spectroscopy of monazite-type ceramics used for nuclear waste conditioning

• Systematic spectroscopic investigations of the lanthanide orthophosphates.
• Improvement of expected linear correlation of infrared wavenumbers versus ionic radii.
• Crystal str. D6 of hydrated LnPO4 is challenged: existence of weak ν1 in IR spectra.
• Discrete fluorescence bands observed in EuPO4 Raman spectrum.

Raman and infrared spectroscopic investigations were performed on synthetic lanthanide orthophosphates (LnPO4) within this study. Seven monoclinic monazite-type phosphates (Ln = La–Gd) were synthesised via precipitation route in aqueous solution at room temperature. Linear correlation between Raman band positions and the effective cationic radii of the Ln3+ was observed. New infrared spectroscopic data confirmed the expected steady increase of the LnPO4 wavenumbers regarding the Ln atomic number.