Synthesis and luminescence properties of ß-NaRE0.95Eu0.05F4 (RE=Y, Lu)

On the base of ss-NaYF4 and ss-NaLuF4 compounds, optimal synthesis methods were selected to obtain highly crystalline Eu3+-doped compounds in the hexagonal (ss) structure. The compounds ss-NaY0.95Eu0.05F4 and ss-NaY0.95Eu0.05F4 were synthesized by hydrothermal synthesis. The concentration of Na2EDTA introduced into the reaction system as a modifier affects the shape and size of the product from elongated hexagonal prisms to quartz-like crystals. The thermal behavior of the compounds has been studied; the temperature of the polymorphic transition from hexagonal to cubic structure is 680 degrees C for ss-NaY0.95Eu0.05F4 and 624 degrees C for ss-NaY0.95Eu0.05F4, the melting point of alpha-NaY0.95Eu0.05F4 is about 900 degrees C. Under excitation with UV-light of lambda = 393 nm, ss-NaY0.95Eu0.05F4 and ss-NaY0.95Eu0.05F4 show the emission lines of direct Eu3+ f-f transitions, with the presence of the emission from higher Eu3+ excited states (up to 5H3) in both samples, which is responsible for the more orange color of emission instead of the usual red for Eu3+. Emission decay times are slightly longer for ss-NaY0.95Eu0.05F4 than for ss-NaY0.95Eu0.05F4, which is the result of a bigger unit cell for the former, leading to longer interatomic distances between Eu3+ ions in the lattice. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed. (C) 2020 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.