Preparation And Luminescence Properties Of Rare-Earth Organic-Inorganic Hybird Material Based On Titania/Alumina Systems

Trivalent rare ions have excellent photoactive properties such as sharp emissionspectra for high color purity, broad emission bands covering the ultraviolet(UV)–visible–nearinfrared (NIR) region, a wide range of lifetimes from themicroseconds to milliseconds level, and high luminescence quantum efficiencies.These properties have attracted much attention for awide variety of applications in thefields of lighting devices, and biomedical analysis. However, it is hard to generateefficient luminescence emission by direct excitation because of the f-f transitions oflanthanide ions are spin forbidden. One can design lanthanide complexes comprisingof sensitizing ligands due to their well-known “antenna effects”. Unfortunately, thepractical application of lanthanide complexes is still limited to a certain extent bytheir poor stability under high temperature, high pressure or moisture conditions, andtheir low mechanical strength. Therefore, in order to improve the photostability oflanthanide complexes, the new concept of ‘‘organic–inorganic hybrid materials’’provides photofunctional lanthanide materials. Rare earth organic–inorganic hybridmaterials have attracted considerable attention because they combine someadvantages of rare earth complexes and inorganic matrix (chemical and thermalstability). However, lanthanide organic complexes containing hybrid materials weremainly developed for silicate systems. The extension of this chemistry to other oxidesthan silica would allow new options for the development of hybrid organic-inorganicmaterials based on lanthanide complexes. Among the oxides, titania and alumina haveattracted much attention as a host matrix for lanthanide complexes because of theirpeculiar and fascinating physicochemical properties and a wide variety of potentialuses in diverse fields. Therefore, the main research results in our work aresummarized as: 1. In this thesis, lanthanide (Eu3+and Tb3+) inorganic-organic hybrid materialswith alumina and titania gels as linkage to be coordinated to2,6-dipicolinic acidwere synthesized via classical sol-gel method,2,6-dipicolinic acid is not only modifythe reactivity of titanium and alumina precursor and coordinate to europium andterbium ions, but also sensitize their luminescence. The character of the hybridmaterials are characterized with SEM, DSC-TG, XRD, FT-IR, and luminescencespectra, as well as luminescence decay analysis. The hybrid materials exhibitexcellent thermal stabilities, stronger luminescence intensities, long fluorescencelifetimes, higher quantum efficiency and show a strong red and greenphotoluminescence upon irradiation with ultraviolet light. The hybrids Eu-DPA-Aland Tb-DPA-Al show a better luminescence than other hybrids, which indicates thatthe Al–O network is a better candidate host for supporting the lanthanide complexthan other network. The effect of the microenvironment, especially the number ofcoordinated water molecules on the luminescence properties are also investigated indetail.2. Recently, we reported an efficient approach for biligand rare earth complexescould be immobilized on alumina and titania materia by sol-gel method, in which itwas can be found that2-pyrazinecarboxylic acid (PZC) as the first-class ligand,tris(2-thenoyltrifluoroacetonato) as second-class ligand, and Eu3+as coordinationatom. The character of the hybrid materials are characterized with SEM, TG, XRD,FT-IR and luminescence spectra, as well as luminescence decay analysis.Especiallythe photoluminescence measurements indicate that the obtained hybrid materialsexhibit characteristic luminescence in different hybrid hosts. The obtained hybridmaterials show a better luminescence compared with that of the pure2-pyrazinecarboxylic acid complexes grafted to the same inorganic components(Ti(OCH(CH3)2)4or Al(OCH(CH3)2)3).