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

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