| Summary: | In the present work, the Tb<sup>3+</sup>/Eu<sup>3+</sup> co-activated sol-gel glass-ceramic materials (GCs) containing MF<sub>3</sub> (M = Y, La) nanocrystals were fabricated during controlled heat-treatment of silicate xerogels at 350 °C. The studies of Tb<sup>3+</sup> → Eu<sup>3+</sup> energy transfer process (ET) were performed by excitation and emission spectra along with luminescence decay analysis. The co-activated xerogels and GCs exhibit multicolor emission originated from 4f<sup>n</sup>–4f<sup>n</sup> optical transitions of Tb<sup>3+</sup> (<sup>5</sup>D<sub>4</sub> → <sup>7</sup>F<sub>J</sub>, J = 6–3) as well as Eu<sup>3+</sup> ions (<sup>5</sup>D<sub>0</sub> → <sup>7</sup>F<sub>J</sub>, J = 0–4). Based on recorded decay curves, it was found that there is a significant prolongation in luminescence lifetimes of the <sup>5</sup>D<sub>4</sub> (Tb<sup>3+</sup>) and the <sup>5</sup>D<sub>0</sub> (Eu<sup>3+</sup>) levels after the controlled heat-treatment of xerogels. Moreover, for both types of prepared GCs, an increase in ET efficiency was also observed (from η<sub>ET</sub> ≈ 16% for xerogels up to η<sub>ET</sub> = 37.3% for SiO<sub>2</sub>-YF<sub>3</sub> GCs and η<sub>ET</sub> = 60.8% for SiO<sub>2</sub>-LaF<sub>3</sub> GCs). The changes in photoluminescence behavior of rare-earth (RE<sup>3+</sup>) dopants clearly evidenced their partial segregation inside low-phonon energy fluoride environment. The obtained results suggest that prepared SiO<sub>2</sub>-MF<sub>3</sub>:Tb<sup>3+</sup>, Eu<sup>3+</sup> GC materials could be considered for use as optical elements in RGB-lighting optoelectronic devices operating under near-ultraviolet (NUV) excitation.
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