Synthesis And Luminescent Properties Of Rare Earths Doped Silica Luminescent Materials With Special Morphologies

Silica materials with special morphologies have attracted significant interest by virtueof their tunable shape, size, and morphology. These materials exihibit a range of optical,electrical and mechanical properties, which are often related to their sizes and structures.The Si-OH moieties on the surface of these materials make them functionalizable usingsimple silane chemistry. Such surface-modified nanomaterials can be useful in catalysis,separation, detection, biolabeling, and biomolecule delivery. In addition to thesurface-related chemistry, the luminescent nature of these amorphous structures hasattributed them with potential applications in optoelectronic devices and optical sensors.Moreover, the attractive features of lanthanide ions as luminescent materials includelinelike emission, high quantum yield, long luminescence lifetime (μs-ms range), highphotochemical stability, and low long-term toxicity. The loading of lanthanide ions withhost materials can offer the advantages of superior mechanical property, betterprocessability, and thermal stability.Pure silica materials and rare earth doped silica materials were prepared by sol-geltranscription from tartaric acid/europium tartrate in different conditions, and characterizedwith different methods. The luminescent properties of silica matrix and dopingconcentration and site of trivalent europium ion were studied deeply.1. Tartaric-templated silica nanotubes were conveniently synthesized by sol-gelmethod. It is found that tartaric templates can form spindle/spherical-like aggregatescomposed of many sheets under static/stirring condition, which lead to the differentshapes of silica nanotubes. The external diameter and wall thickness of both products are300~400nm and70~150nm, respectively. Hydrogen-bond interaction,supramolecular interaction and a competition of various effects may be the reasons of thenanotubes formation. Moreover, under ultraviolet light excitation, the silica nanotubesexhibited blue emission and luminescent intensity of the tubes prepared under the static condition is much stronger than the stirring ones, mostly because of more defect centersin the structures obtained under stirring condition.2. Photoluminescent silica nanotubes were conveniently synthesized by using sol–gelmethod, in which europium ions entered silica matrix. The nanotubes had a length ofseveral microns. The wall thickness, inner and outer diameters of nanotubes are in therange of30~100,100~200and200~300nm，respectively. The results indicated thateuropium tartrates nanofibers as a template can transform tetraethylorthosilicate intosilica nanotubes effectively. Meanwhile, europium ions were transferred from the fibersto the tubes successfully. A hard template mechanism was proposed to explain theformation process of Eu3+-doped silica nanotubes. Photoluminescence spectra ofphotoluminescent silica nanotubes revealed trivalent europium ion emission characteristicand13%was the quenching concentration of europium ions in silica matrix for thissystem.3. Eu3+-doped silica nanowires were synthesized by varying the hydrolysis andcondensation rate of TEOS with the growth of nanofibers, and the situation of europiumin the silica matrix was investigated. The length and diameter of nanotubes were in therange of several microns and50~200nm，respectively. The characterization of energydispersive X-ray elemental distribution maps, Fourier transform infrared spectra andX-ray photoelectron spectroscopy were indicative of the presence of covalent Si-O-Eu.The results suggested that the europium ions are doped in the amorphous silicasuccessfully. Furthermore, a sol-gel inorganic-organic co-assembly mechanism wasproposed to explain the formation process of Eu3+-doped silica nanowires. In addition,photoluminescent emission of europium ions in silica matrix was further discussed. It wasindicated that10%is the quenching concentration of Eu3+in the system and the siteenvironment of Eu3+in the nanowires annealed at650oC has high luminescence intensitydue to silica network structure.4. Hollow Eu3+-doped silica flower-like microspheres with several microns range of diameter were prepared in ethanol solution. The microspheres with hollow structure aftercalcination had a diameter of2.5μm and shell of500nm, which morpholory was similarto europium tartrate templates. It was proved that Eu3+ions existed in the form ofSi-O-Eu covalent bond by energy dispersive X-ray elemental distribution maps, Fouriertransform infrared spectra and X-ray photoelectron spectroscopy. Furthermore, a sol-geltemplated mechanism is proposed to interpret the formation process of flower-likemicrospheres shape. In addition, photoluminescent emission of the products was furtherdiscussed, which indicated that Eu3+ions exhibit characteristic luminescent emissions andtheir luminescent intensity and peak shape after calcination was higher and wider thanas-synthesized sample.