Synthesis and luminescence properties of β-NaRE0.95Eu0.05F4 (REY, Lu)

• Published in: Journal of industrial and engineering chemistry (Seoul, Korea) Vol. 92; pp. 218 - 225
• Main Authors: Razumkova, Illariia A., Sedykh, Alexander E., Denisenko, Yuriy G., Müller-Buschbaum, Klaus
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25-12-2020; 한국공업화학회
• Subjects: Luminescence properties; Rare earth fluoride; Synthesis; 화학공학; Luminescence properties; Rare earth fluoride; Synthesis
• ISSN: 1226-086X; 1876-794X
• DOI: 10.1016/j.jiec.2020.09.008

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•An environmentally friendly synthesis of β- NaRE0.95Eu0.05F4 (RE=Y, Lu) from an aqueous solution by hydrothermal synthesis was elaborated.•The concentration of Na2EDTA control the morphology of the compound NaY(Lu)0.95Eu0.05F4.•The excitation spectra of β-NaRE0.95Eu0.05F4 (RE=Y, Lu) consist of direct f–f Eu3+ transitions, the most intense being 5L6 ⟵ 7F0 at 393nm.•The presence of emission from higher excited states of Eu3+ in both samples results in an emission color being more orange than the usual..
On the base of β-NaYF4 and β-NaLuF4 compounds, optimal synthesis methods were selected to obtain highly crystalline Eu3+-doped compounds in the hexagonal (β) structure. The compounds β-NaY0.95Eu0.05F4 and β-NaLu0.95Eu0.05F4 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°C for β-NaY0.95Eu0.05F4 and 624°C for β-NaY0.95Eu0.05F4, the melting point of α-NaRE0.95Eu0.05F4 is about 900°C. Under excitation with UV-light of λ = 393nm, β-NaY0.95Eu0.05F4 and β-NaLu0.95Eu0.05F4 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 β-NaY0.95Eu0.05F4 than for β-NaLu0.95Eu0.05F4, 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.