Unusual Eu 3+ Luminescent Properties in Alkaline Lanthanum Fluorogermanate Glasses and Glass–Ceramics
Raphael Rodrigues Faleiros, Ana Flávia Teófilo Da Silva, Yago Langer Campos de Lima, Fabia Castro Cassanjes, Marc Dussauze, Thierry Cardinal, Lauro June Queiroz Maia, Gael PoirierABSTRACT
Lanthanum fluorogermanate glass samples were prepared by melt‐quenching in ternary compositions 55GeO 2 –15M 2 O–30LaF 3 , M being K or Na and doped with 0.25 mol% of Eu 2 O 3 . Thermal analysis by differential scanning calorimetry (DSC) technique allowed us to determine both glass transition and crystallization temperatures in bulk and powder samples. Heat treatments (HTs) were performed on the basis of DSC curves with increasing HT time and temperature, and glass–ceramics were obtained in both systems. In the potassium‐based glass composition, cubic KLaF 4 is precipitated for lower HT temperatures. However, for the sodium‐based glass, hexagonal NaLaF 4 is first precipitated at lower temperatures, whereas hexagonal fluorecite LaF 3 is also crystallized at higher temperatures. Eu 3+ spectroscopy identified strong emission dependency with the crystallization state and nature of crystalline phases. Emission bands related to electronic transitions from the 5 D 2 and 5 D 1 , usually not observed in oxide and even oxyfluoride glasses, were clearly identified and with relative strong intensity together with the well‐known Eu 3+ red emissions, pointing out unusual effective Eu 3+ blue and green emission in these glass–ceramics. Experimental lifetimes were useful to identify different Eu 3+ sites related with oxide/fluoride as well as glassy/crystalline environments.