Solvothermal chemistry of luminescent lanthanide fluorides
Abstract
Exploration of novel lanthanide fluoride framework materials in inorganic-organic hybrid
systems under solvothermal conditions towards development of new luminescent
materials is discussed. X-ray single crystal and powder diffraction methods have been
used as crystallographic characterisation techniques. Determination and study of
luminescence 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 framework
incorporating 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 vertex
sharing (InF₅)[subscript(∞)] chains, which are linked via H-bonded organic moieties. The scandium
and fluorine local environments of [C₄H₁₄N₂][ScF₅] are characterised by ¹⁹F, and
⁴⁵Sc
solid-state MAS NMR spectroscopies. A single scandium site has been confirmed by
⁴⁵Sc
MAS NMR. ¹⁹F MAS NMR clearly differentiates between bridging and terminal
fluorine. 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⁺ doped
samples occurs at x = 0.05 Eu³⁺ and the “asymmetry ratio” of R = I₅₉₀/I₆₁₅ (
⁵D₀ →
⁷F₂ and
⁵D₀ →
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 to
⁵D₄ →
⁷F₅ (green at 543.5 nm) occurs. In addition, a Tb³⁺/Eu³⁺ co-doped sample exhibits a
combination of green (Tb³⁺) and orange (Eu³⁺) luminescence, with Tb³⁺ enhancing the
emission of Eu³⁺ in this host.
Exploration of novel indium, aluminium, and zirconium fluoride crystal structures with
potential luminescent properties has also been undertaken. A chiolite-like phase K₅In₃F₁₄
(space group P4/mnc) has been synthesised. No phase transition occurs over the
temperature range 113K< T< 293 K, as has been seen in other chiolite-like structures. An
organically templated indium fluoride, [NH₄]₃[C₆H₂₁N₄]₂[In₄F₂₁] has been prepared; this
features 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 Sr
²⁺ this may be a potential host for
blue luminescent Eu²⁺. The new material KZrF₅.H₂O shows pentagonal-bipyramidal
geometry of Zr⁴⁺ with a polar space group, Pb2₁m, which may potentially have
ferroelectric properties.
Type
Thesis, PhD Doctor of Philosophy
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