Solvothermal chemistry of luminescent lanthanide fluorides

Fluorides;Rare earth metals;Luminescence;High temperature chemistry

Jayasundera, Anil ; Lightfoot, Philip ; Lightfoot, Philip

University:University of St Andrews

Department:Chemistry (School of)

关键词: Fluorides;    Rare earth metals;    Luminescence;    High temperature chemistry;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/2125/AnilJayasunderaPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

Exploration of novel lanthanide fluoride framework materials in inorganic-organic hybridsystems under solvothermal conditions towards development of new luminescentmaterials is discussed. X-ray single crystal and powder diffraction methods have beenused as crystallographic characterisation techniques. Determination and study ofluminescence properties for selected hybrid materials has also been carried out.The first organically templated luminescent lanthanide fluoride framework, [C₂N₂H₁₀]₀.₅[Ln₂F₇] (Ln= Nd, Tb, Dy, Ho, Er, Yb and Lu), has been synthesised and characterised.This structure type consists of a three-dimensional yttrium fluoride frameworkincorporating two similar, but crystallographically distinct, yttrium sites.Photoluminescence studies of [C₂N₂H₁₀]₀.₅ [Y₂F₇]: Ln³⁺ (Ln³⁺ = Gd³⁺, Eu³⁺ and Tb³⁺)have been explored and characteristic luminescence emissions are reported.An inorganic-organic hybrid indium fluoride and its scandium fluoride analogue,[C₄H₁₄N₂][MF₅](M=In and Sc) is reported. The structure consists of infinite trans vertexsharing (InF₅)[subscript(∞)] chains, which are linked via H-bonded organic moieties. The scandiumand fluorine local environments of [C₄H₁₄N₂][ScF₅] are characterised by ¹⁹F, and⁴⁵Scsolid-state MAS NMR spectroscopies. A single scandium site has been confirmed by⁴⁵ScMAS NMR. ¹⁹F MAS NMR clearly differentiates between bridging and terminalfluorine. The photoluminescence properties of these complexes, [C₄H₁₄N₂][In[subscript(1-x)] Ln[subscript(x)]F₅](Ln=Tb and/or Eu), have been explored. The optimum composition for Eu³⁺ dopedsamples occurs at x = 0.05 Eu³⁺ and the “asymmetry ratio” of R = I₅₉₀/I₆₁₅ (⁵D₀ →⁷F₂ and⁵D₀ →⁷F₁) gives a clear picture of the sensitivity for crystal field of the compound.For x = 0.08 Tb³⁺, a strong down-conversion fluorescence corresponding to⁵D₄ →⁷F₅ (green at 543.5 nm) occurs. In addition, a Tb³⁺/Eu³⁺ co-doped sample exhibits acombination of green (Tb³⁺) and orange (Eu³⁺) luminescence, with Tb³⁺ enhancing theemission of Eu³⁺ in this host.Exploration of novel indium, aluminium, and zirconium fluoride crystal structures withpotential luminescent properties has also been undertaken. A chiolite-like phase K₅In₃F₁₄(space group P4/mnc) has been synthesised. No phase transition occurs over thetemperature range 113K< T< 293 K, as has been seen in other chiolite-like structures. Anorganically templated indium fluoride, [NH₄]₃[C₆H₂₁N₄]₂[In₄F₂₁] has been prepared; thisfeatures the trimeric unit [In₃F₁₅]³⁻ which appears to be the first of its type in a metal fluoride. A new hybrid fluoride, Sr[N₂C₂H₁₀]₂[Al₂F₁₂].H₂O has been synthesised.Because the ionic radius of Eu²⁺ is similar to that of Sr²⁺ this may be a potential host forblue luminescent Eu²⁺. The new material KZrF₅.H₂O shows pentagonal-bipyramidalgeometry of Zr⁴⁺ with a polar space group, Pb2₁m, which may potentially haveferroelectric properties.