Dynamical processes of Ln³⁺ ions doped in LaF₃ nanocrystals embedded in transparent oxyfluoride glass

The transverse and longitudinal relaxations from the excited electronic levels of rare earth ions (Ln³⁺) in nanocrystals are reviewed. Employing the frequency up-converted emission, we have studied the ion-ion interactions and the distribution of the ions within Pr³⁺:LaF ₃ nanocrystals embedded in oxyfluoride glass. The phonon-assisted energy transfer between Pr³⁺ ions is discussed and the relation between the energy transfer rate and the buildup of the up-converted emission is established. The results suggest that the Pr³⁺ concentration inside the nanocrystals is 5-10 times that of the average concentration. A jump in the energy transfer rate is observed as the concentration increases, and the possible processes behind it are discussed.