Fabrication of lanthanide decatungstate [LnIII/IV(W5O18)2]8−/9− (Ln = CeIV/III, EuIII, and ErIII) thin films using spin-coating from aqueous solutions

Lanthanide decatungstate Nam[Ln(W5O18)2]·nH2O (LnW10: m = 9 for Ln = EuIII, CeIII, and ErIII; m = 8 for Ln = CeIV) thin films were fabricated on quartz glass substrates by spin-coating using water as the solvent. In this method, we exclude hybrids with organic materials to avoid undesirable modification of the original photophysical properties of LnW10. The resultant films were characterized by X-ray diffraction (XRD), scanning probe microscopy (SPM), optical absorption, and photoluminescence spectroscopy. All the films had high transparency, flatness, and homogeneity. The thickness of the films was controllable by adjusting the concentration of LnW10 solution. XRD measurements showed that the [LnIII/IV(W5O18)2]9−/8− molecules in all the films were self-organized, forming a layer-like periodic structure with a periodicity of ∼14 Å in the early stage, followed by time-dependent structural changes. The EuIIIW10 film exhibited photoluminescence upon excitation at ∼250 nm; the film's spectrum and lifetime were similar to those of the crystal sample. These results demonstrate that the molecular environment in LnW10 thin films is similar to that found in solid crystals.

► Lanthanide decatungstate (LnW10) thin-films were fabricated by a spin-coating method.
► We obtained transparent films of good quality without hybrid with organic cations.
► A self-organized periodic structure was formed spontaneously.
► Optical and luminescence properties were similar to those of LnW10 (Ln = Eu) crystals.