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 Na 9EuW 10O 36 or Na 9SmW 10O 36. The above results indicate that the monolayer of DODA has a strong interaction with the polyanions of EuW 10O 36 9− (or SmW 10O 36 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 EuW 10O 36 9− can give off strong fluorescence on UV irradiation. The characteristic emission behaviors of europium ions in LB films and in the powder of Na 9EuW 10O 36 are discussed. It is found that the intensity ratio of the 5D 0→ 7F 2 transition to the 5D 0→ 7F 1 transition in LB film is quite different from that in the powder of Na 9EuW 10O 36. 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.