Fabrication of lanthanide decatungstate [Ln~(III/IV) (W_5O_(18))_2]~(8-/9-) (Ln = Ce~(IV/III), Eu~(III), and Er~(III) thin films using spin-coating from aqueous solutions

摘要

Lanthanide decatungstate Na_m[Ln(W_5O_(18))_2]-nH_2O (LnW_(10): m = 9 for Ln = Eu~(III), Ce~(III), and Er~(III); m = 8 for Ln = Ce~(IV)) 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 LnW_(10). The resultant films were characterized by X-ray diffraction (XRD), scanning probe microscopy (SPM), optical absorption, and photoluminescence spectroscopy. Ail the films had high transparency, flatness, and homogeneity. The thickness of the films was controllable by adjusting the concentration ofLnW_(10) solution. XRD measurements showed that the [Ln~(III/IV)(W_5O_(18))_2]~(9-/8-) molecules in all the films were self-organized, forming a layer-like periodic structure with a periodicity of ~14A in the early stage, followed by time-dependent structural changes. The Eu~(III)W_(10) film exhibited photoluminescence upon excitation at ~250nm; the film's spectrum and lifetime were similar to those of the crystal sample. These results demonstrate that the molecular environment in LnWio thin films is similar to that found in solid crystals.