Preparation And Fluorescence Properties Based On Europium-substituted Polyoxometalates

Polyoxometalates (POMs) including Ln elements such as Sm³⁺, Eu³⁺, Tb³⁺ and Dy³⁺ are of special interest as they can produce strong fluorescence, high fluorescent efficiency, very sharp emission bands, long decay times and excellent monochromatocity, especially high thermal stability. Due to above characters, Ln complexes are good candidates for various electronic, magnetic, Lewis acid catalytic centers, especially for luminescent materials. Regarding different POMs incorporating Eu ions (Eu-POMs) as raw materials, the Eu-POMs/PVA complex materials with different morphological were prepared by different techniques. The photoluminescent behaviors of the Eu-POMs complex materials with different morphological were discussed.1. Using float-prolonging technique, the ultra-thin film were prepared, including EuW10/PVA,EuPW11/PVA,EuSiW11/PVA与EuP2W17/PVA. FT-IR spectra and UV-Vis spectra indicated that the Eu-POMs/PVA ultra-thin film kept in good agreement with original compounds, meanwhile, they also showed the presence of intermolecular bonding between Eu-POMs and PVA. Different photoluminescent behaviors of Eu-POMs/PVA were explored and researched, either.2. Using electrospinning method,the Eu-POMs/PVA the ultra-fine fiber mats were prepared. Datas of FT-IR spectra and UV-Vis spectra indicated that the Eu-POMs/PVA ultra-fine fiber mats kept in good agreement with original compounds, meanwhile, they also showed the presence of intermolecular bonding between Eu-POMs and PVA. Scanning electron microscopy (SEM) showed the Eu-POMs/PVA ultra-fine fiber mats with smooth surfaces without droplet and random oriented nanometer-scale. The diameters were in the range of 200 to 600 nm. Fluorescence spectra showed perfect photoluminescent behaviors in the ultra-fine fiber mats.3. Improving traditional electrostatic layer-by-layer (LBL) technique, electrospun PVA nanofibers mat was collected on indium tin oxide (ITO) substrate. Heat crosslinked nanofibersmat became water-insoluble and firmly fixed on ITO substrate even in water. Oppositely charged poly (allylamine hydrochloride) (PAH) and Eu-POMs were alternately assembled on PVA nanofibers-coated ITO substrate to construct multilayers film through LBL technique. Using this method, we prepared (EuW10/PAH)10,(EuPW11/PAH)10,(EuSiW11/PAH)10与(EuP2W17/PAH)10 multilayer film. The SEM images showed that EuPW11 multilayer film was selectively deposited on PVA nanofibers because the electrospun nanofibers have larger surface area and surface energy than that of the flat substrate. The cyclic voltammograms current responses of the EuPW11 multilayer film on PVA/ITO electrode were used to monitor the deposition process. Fluorescence spectra showed perfect photoluminescent behaviors of the (Eu-POMs/PAH)10/PVA/ITO multilayers film.