Study on highly ordered luminescent Langmuir-Blodgett films of heteropolytungstate complexes containing lanthanide

Luminescent thin films of heteropolytungstate complexes containing lanthanide (europium or samarium) were successfully fabricated by the Langmuir-Blodgett (LB) technique. The pressure-area isotherm of the monolayer of dimethyldioctadecylammonium bromide (DODA) is modified rather markedly when the subphase contains the complex of Na₉EuW₁₀O₃₆ or Na₉SmW₁₀O₃₆. The above results indicate that the monolayer of DODA has a strong interaction with the polyanions of EuW₁₀O₃₆^9- (or SmW₁₀O₃₆^9-). X-ray photoelectron spectra and fluorescent spectra verify that europium and tungsten atoms are incorporated into the LB films. Ultraviolet (UV), fluorescent spectra and low-angle X-ray diffraction experiments demonstrate that these LB films have a well-defined lamellar structure. The LB film containing EuW₁₀O₃₆^9- can give off strong fluorescence on UV irradiation. The characteristic emission behaviors of europium ions in LB films and in the powder of Na₉EuW₁₀O₃₆ are discussed. It is found that the intensity ratio of the ⁵D₀ → ⁷F₂ transition to the ⁵D₀ → ⁷F₁ transition in LB film is quite different from that in the powder of Na₉EuW₁₀O₃₆. The difference of the ratio indicates that the site symmetry of europium is distorted in LB film, which is probably due to the strong electrostatic interactions between DODA and polyanions.