Energy Transfer Study on Tb 3+ /Eu 3+ Co-Activated Sol-Gel Glass-Ceramic Materials Containing MF 3 (M = Y, La) Nanocrystals for NUV Optoelectronic Devices.

In the present work, the Tb ³⁺ /Eu ³⁺ co-activated sol-gel glass-ceramic materials (GCs) containing MF ₃ (M = Y, La) nanocrystals were fabricated during controlled heat-treatment of silicate xerogels at 350 °C. The studies of Tb ³⁺ → Eu ³⁺ 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 ⁿ -4f ⁿ optical transitions of Tb ³⁺ ( ⁵ D ₄ → ⁷ F _J , J = 6-3) as well as Eu ³⁺ ions ( ⁵ D ₀ → ⁷ F _J , J = 0-4). Based on recorded decay curves, it was found that there is a significant prolongation in luminescence lifetimes of the ⁵ D ₄ (Tb ³⁺ ) and the ⁵ D ₀ (Eu ³⁺ ) 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 _ET ≈ 16% for xerogels up to η _ET = 37.3% for SiO ₂ -YF ₃ GCs and η _ET = 60.8% for SiO ₂ -LaF ₃ GCs). The changes in photoluminescence behavior of rare-earth (RE ³⁺ ) dopants clearly evidenced their partial segregation inside low-phonon energy fluoride environment. The obtained results suggest that prepared SiO ₂ -MF ₃ :Tb ³⁺ , Eu ³⁺ GC materials could be considered for use as optical elements in RGB-lighting optoelectronic devices operating under near-ultraviolet (NUV) excitation.