SECONDMENTS

Trivalent lanthanide ions (Ln3+) are well-known for having unique optical properties, presenting narrow long-lived emission bands that cover the entire electromagnetic spectrum. Among the Ln3+ available, Tb3+ stands out because it presents a high magnetic moment and a characteristic green emission, leading to materials with interesting magnetic and optical properties. The incorporation of Tb3+ into glasses is particularly attractive because it paves the way for the development of optical isolators, information storage devices, and magneto-optical fiber sensors. Borogermanate glasses are commonly used for the preparation of such materials because they can hold a high content of Ln3+, allowing to tailor the optical and magnetic properties towards the desired application. In this way, this secondment focused on the preparation of borogermanate luminescent glasses to combine the magnetic properties with thermal sensing through luminescence thermometry.

• Preparation of borogermanate luminescent glasses
• Preliminary optical characterization

The preparation of the magneto-optical glasses was performed during the first week of the secondment. Terbium doped borogermanate glasses were obtained through the melt-quenching method, presenting the characteristic green emission of Tb3+ under excitation with ultraviolet light. In the second week, the preliminary optical characterization was performed through UV-Vis, m-lines, and photoluminescence spectroscopy to access the transparency, refactive index, and luminescent properties of the glasses, respectively. Figure 1 sums up the characterization performed during the secondment.

The expertise of the researchers at the Host Institution was essential for obtaining the magneto-optical glasses in such a short period. Good training in the synthesis of glass by using the melt-quenching method was provided, allowing the preparation of the luminescent glasses, as well.

The next steps regarding the project rely on the advanced optical characterization of the glasses based on temperature-dependent photoluminescence measurements at CICECO. Another secondment period is expected to obtain optical fibers from the same materials.

Figure 1. Transmittance spectrum (A) and refractive index (B) of the obtained borogermanate glasses. Excitation spectrum of sample BGB-4Tb monitoring the emission at 545 nm (C) and emission spectra of different terbium-doped borogermanate glasses under excitation at 375 nm (D). The inset in panel D shows the characteristic green color of Tb³⁺ under UV light exposure (365 nm) in the sample BGB-4Tb.