Fabrication of luminescence-sensing films based on surface precipitation reaction of Mg–Al–Eu LDHs

Abstract

Amorphous Mg–Al–Eu–O thin films were prepared on silica glass substrates by a sol–gel dip-coating method with a heat treatment at 700 °C. Immersion of the oxide thin films in water or aqueous solutions at 90 °C resulted in precipitation of Mg–Al–Eu-layered double hydroxides around the film surface. Eu3+ ions doped in the oxide thin films exhibited photoluminescence by irradiation with ultraviolet light. Photoluminescence intensity was decreased after the immersion of the oxide thin films in water, which was associated with the precipitation of carbonate-intercalated layered double hydroxides. In contrast, when using aqueous solutions containing organic acid salts such as sodium benzoate or disodium terephthalate, photoluminescence intensity was remarkably increased after the immersion due to the precipitation of benzoate-intercalated or terephthalate-intercalated layered double hydroxides. The enhanced photoluminescence property was explained by the antenna effect with an efficient energy transfer from the intercalated anions to the Eu3+ ions. A possibility of applying this phenomenon to luminescence sensing was investigated using various conditions for the immersion of the thin films.