| The design and characterization of new materials capable of converting low-energy photons input into discrete higher-energy luminescence (i.e. UC) have received great attention due to the possibilities of utilizing these materials to achieve short wavelength laser, sensor, color display and infrared viewer. However, up-conversion luminescence efficiency is not very high, how to improve the up-conversion luminescence efficiency has become a topic of widespread concern. Choose a suitable UC host materials can greatly improve the up-conversion luminescence efficiency. Hexagonal wurtzite ZnO is a promising one for visible and infrared UC phosphor as the wide band gap ZnO has no absorption in the range of our interest, moreover the phonon energy of ZnO is relatively low, which has great influence on the UC properties. TiO2as a stable(fusion point1830℃), nontoxic, anticorrosive, wide band gap(rutile:3.0eV and anatase:3.2eV) semiconductors, moreover the phonon energy of TiO2is relatively low, which shown great potential applications for UC phosphor.In this paper, rare earth ion Er3+and Yb3+are incorporated into the ZnO and TiO2lattice successfully, afterwards parts of which are separated and surface modified, the detail is discussed:1. Core/shell ZnO:Er3+-Yb3+/Gd2O3nanoparticles are synthesized in solution phase via seeded deposition process using about40-70nm ZnO:Er3+-Yb3+nanoparticles as seeds and Gd(NO3)3as Gd-source respectively. Analyses on phase and structure based on X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques indicate that the Gd2O3shell is around1nm in thickness. At the same time, a typical HRTEM image of sample E is shown the core is perfectly periodic arrangement with lattice constant of a=3.31A, which is slightly larger than that of the bulk owning to the larger radius of Er3+and Yb3+than that of Zn2+, while the shell is polycrystalline, coving on the core. Upon excitation by980nm SLD, all the samples display UC emissions (red and green) that could be seen with naked eyes. From the UC spectra we can see that the peaks locating in the range of515-538nm,538-567nm, and646-674nm originate from transitions2H11/2-4I15/2,4S3/2-4I15/2and4F9/2-4I15/2, respectively. It is obvious that the after Gd2O3surface modification of96h, red and green intensity of UC emission is increased by17.9and149.6times, respectively and the intensity of green to red ratio (GRR) is improved greatly by Gd2O3treatment, changing from0.036to0.298, this material is a promising up-conversion luminescence material, up-conversion luminescence material could be useful for enhancing the efficiency of current solar cells, and in other areas such as displays,3D recording data, biological labels and visible solid state lasers.2. Er3+-Yb3+co-doped TiO2nanoparticles (NPs) embedded in amorphous matrix with varying Yb3+concentrations are fabricated by a sol-gel method, afterwards parts of which are separated and surface modified in Mo(NO3)3solution. The effect of Yb3+doping concentrations on luminescent properties of TiO2nanoparticles was studied in detail. Analyses on phase and structure indicate that Er3+and Yb3+are incorporated into the TiO2lattice successfully, a NP is single crystal that is surrounded by amorphous matrix. Before surface modification the intensity of the emission first increase and then decrease with the increase of Yb3+concentration. After MoO3surface modification, the intensity of the emissions increase, however the optimal concentration of Yb3+for UC this time is not5%but10%with modification time of24h. Upon excitation by980nm SLD, all the samples display UC emission which could be seen with naked eyes. This finding is interesting and has potential applications in solar cells, photonic crystals, etc. |
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