Energy Transfer Study on Tb3+/Eu3+ Co-Activated Sol-Gel Glass-Ceramic Materials Containing MF3 (M = Y, La) Nanocrystals for NUV Optoelectronic Devices.

In the present work, the Tb3+/Eu3+ co-activated sol-gel glass-ceramic materials (GCs) containing MF3 (M = Y, La) nanocrystals were fabricated during controlled heat-treatment of silicate xerogels at 350 °C. The studies of Tb3+ → Eu3+ 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 4fn-4fn optical transitions of Tb3+ (5D4 → 7FJ, J = 6-3) as well as Eu3+ ions (5D0 → 7FJ, J = 0-4). Based on recorded decay curves, it was found that there is a significant prolongation in luminescence lifetimes of the 5D4 (Tb3+) and the 5D0 (Eu3+) levels after the controlled heat-treatment of xerogels. Moreover, for both types of prepared GCs, an increase in ET efficiency was also observed (from ηET ≈ 16% for xerogels up to ηET = 37.3% for SiO2-YF3 GCs and ηET = 60.8% for SiO2-LaF3 GCs). The changes in photoluminescence behavior of rare-earth (RE3+) dopants clearly evidenced their partial segregation inside low-phonon energy fluoride environment. The obtained results suggest that prepared SiO2-MF3:Tb3+, Eu3+ GC materials could be considered for use as optical elements in RGB-lighting optoelectronic devices operating under near-ultraviolet (NUV) excitation.