Colour tuning in Eu/Ag- co-doped transparent LaF₃ glass-ceramics

Eu/Ag-co-doped transparent oxyfluoride glass-ceramics based on LaF₃ have been obtained by melt-quenching followed by structural analysis employing X-ray diffraction and transmission electron microscopy. Absorption spectra showed only Eu³⁺ ion transitions, irrespective of the presence of silver or the atmosphere used in the preparation. Excitation spectra obtained by collecting luminescence at 437 nm (Eu²⁺) and 612 nm (Eu³⁺) indicated the partial reduction of Eu³⁺ to Eu²⁺. As a consequence, by tuning the excitation wavelength, a variety of emission spectra are obtained, highlighting the coexistence of Eu²⁺ and Eu³⁺ ions, with the emission dominance of the type of ion dependent on the excitation wavelength. The presence of Ag and the atmosphere used during sample preparation affected the intensity of certain emissions, indicating the presence of oxidation-reduction reactions. Chromaticity diagrams illustrating the changes in colour coordinates corresponding to variations in the excitation wavelength showed a range of colours from red to blue, including purple-blue tones.