Electrodeposition Of Rare-earth Luminescent Materials And The Study Of Their Luminescence Properties

Owing to their abundant energy level transition and light conversion modes, rare-earth ions have been widely used in luminescent materials. With intense and long-life luminescence, rare-earth luminescent materials have potential application in fields of laser, display, lighting and biological label. Recently, rare-earth luminescent materials have attracted considerable research interest because of these extensive usages.Compared with other techniques, electrodeposition is a facial method with many advantages, such as low process temperature, low cost, and capability of controlling grain size, morphology and chirality of the deposited films. Rare-earth doped CaF2, NaYF4and LaPO4films have been synthesized by electrodeposition, and their structure, morphology, down-conversion and up-conversion luminescent properties have been discussed. The content of this thesis are listed as following:(1) Electrodeposition and characterization of CaF2and CaF2:Ln3+films:The solutions containing Ca2+-EDTA and NH4F have been used as reactor and CaF2films have been prepared on ITO electrode through anode electrochemical generated acid in solutions. H+ions are generated by the electrochemical oxidation of ascorbate anion instead of water, which is beneficial to cut down the oxidation potential. The released H+ions will lower the pH at the surface of working electrode. Calcium ions are set free from the Ca2+-EDTA complex and then react with F" ions to form CaF2deposits. CaF2and CaF2:Ln3+films are characterized by SEM, XRD, EDS and FL. The CaF2films are composed of spheres, and we also explore the reasons of the morphology. It has been proved that rare earth ions are uniformly distributed in the films by EDS mapping. CaF2:Ln3+films possess not only good down-conversion but also up-conversion properties.(2) Up-conversion fluorescence of lanthanide doped NaYF4films synthesized by electrodeposition:Lanthanide doped NaYF4films have been synthesized by electrodeposition and their up-conversion properties have been studied deeply. Up-conversion (UC) is a process that low energy light, usually near-infrared (NIR), is converted to ultraviolet (UV) or visible by multiple absorptions. When excited at980nm in near-infrared region, NaYF4:Yb3+,Er3+emit intense green and red light, and factors affecting the ratio of green to red are explored in the experiments. Furthermore, it is proved that two-photon up-conversion mechanism is involved in the emission of green and red light. NaYF4:Yb3+,Tm3+film has also been synthesized and it emits bright blue light. The optical properties of down-conversion materials, such as NaYF4:Eu3+and NaYF4:Tb3+, have been studied by photoluminescence (PL) spectra and phenomenon of concentration quenching has been observed.(3) Synthesis and luminescent properties of LaPO4and LaPO4:Ln3+nanorods: LaPO4and LaPO4:Ln3+nanostructures composed of interlaced nanorods or nanowires have been electrodeposited on tin doped indium oxide (ITO) substrate through electrochemical generation of acid in aqueous solutions without any surfactant, catalyst, or template. LaPO4nanorods can be indexed to hexagonal phase by XRD and they are single crystal like structure by electron diffraction (SAED). The optical properties of LaPO4:Ln3+nanostructures have been characterized by PL, and among them LaPO4:Ce3+,Tb3+shows a commercial value. In this material, Ce3+ions act as sensitizer and Tb3+ions act as activator. Due to efficient energy transfer between them, bright green light could be observed.