Synthesis of carboxylate-intercalated layered yttrium hydroxides by anion exchange reactions and their application to Ln³⁺-activated luminescent materials

Layered yttrium hydroxide compounds based on Eu³⁺-and/or Tb³⁺-doped Y₂(OH)₅NO₃ • nH₂O were synthesized in aqueous solutions containing hexamethylenetetramine. Nitrate ions were then exchanged with carboxylate ions such as 4-biphenylacetate (BPA), benzoate, terephthalate, maleate, or oxalate, which were successfully intercalated between yttrium hydroxide layers. While the initial Eu³⁺- or Tb³⁺-doped nitrate samples suffered from relatively low photoluminescence (PL) intensity, those intercalated with BPA, benzoate, terephthalate, or oxalate ions showed considerably enhanced PL intensity, accompanying with broad excitation bands at around 220 - 300 nm. This enhancement was explained with the so-called antenna effect of the organic species. In the Eu³⁺-Tb³⁺-codoped samples, the antenna effect worked similarly for Eu³⁺ and Tb³⁺, thereby resulting in their simultaneous emissions at a single excitation wavelength.