The Effect of Fluorides (BaF₂, MgF₂, AlF₃) on Structural and Luminescent Properties of Er³⁺-Doped Gallo-Germanate...

The effect of BaF₂, MgF₂, and AlF₃ on the structural and luminescent properties of gallo-germanate glass (BGG) doped with erbium ions was investigated. A detailed analysis of infrared and Raman spectra shows that the local environment of erbium ions in the glass was influenced mainly by [GeO]₄ and [GeO]₆ units. Moreover, the highest number of non-bridging oxygens was found in the network of the BGG glass modified by MgF₂. The ²⁷Al MAS NMR spectrum of BGG glass with AlF₃ suggests the presence of aluminum in tetra-, penta-, and octahedral coordination geometry. Therefore, the probability of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ions increases in the BGG + MgF₂ glass system. On the other hand, the luminescence spectra showed that the fluoride modifiers lead to an enhancement in the emission of each analyzed transition when different excitation sources are employed (808 nm and 980 nm). The analysis of energy transfer mechanisms shows that the fluoride compounds promote the emission intensity in different channels. These results represent a strong base for designing glasses with unique luminescent properties.