Studies On Synthesis And Photoluminescence Properties Of Rare Earth/Transition Metal Doped Luminescent Nanomaterials

Recently, luminescent nanomaterials have become the focus in the field of modern nanoscience and nanotechnology, owing to their nanoscale properties which can find many advantages comparing with bulk luminescent materials. Investigating various novel luminescent nanomaterials, developing new synthesis methods and analyzing their luminescent properties are significant to basic research and development of the application of new materials. In this dissertation, valuable exploration have been carried out on the synthesis of new type rare earth/transition metal ions doped nanomaterials as well as their formation mechanism and their novel luminescent properties. The significant results achieved in this dissertation are given as follows:1. Tb³⁺ doped amorphous SiO₂ nanowires have been successfully synthesized by a vapor-liquid-solid (VLS) mechanism. The morphology and composition of the doped nanowires have been characterized. Photoluminescence properties of pure SiO₂ nanowires and Tb doped SiO₂ nanowires with different doping concentration have been investigated, respectively. It shows that pure SiO₂ nanowires have a broad green emission band which is related to the hydrogen-related species (≡Si-H and≡Si-OH); while Tb³⁺ doped SiO₂ nanowires have novel green emissions both from the doped Tb³⁺ ions and the host SiO₂ nanowires. The relationship between the two kinds of emissions has also been investigated. These Tb doped amorphous SiO₂ nanowires exhibit great potential to act as a novel green-emitting phosphor.2. Aluminium borate (Al₁₈B₄O₃₃) nanorods doped with Eu³⁺ and Eu²⁺ have been synthesized via a simple calcination method. A self-catalytic growth mechanism is proposed for the synthesis of the doped nanorods. Photoluminescence measurements indicate that Al₁₈B₄O₃₃:Eu³⁺ nanorods exhibit red emission originating from the ⁵D₀→⁷F₂ electric dipole transition in Eu³⁺ ion, and Al₁₈B₄O₃₃:Eu²⁺ nanorods display a broad green emission band corresponding to the 4f⁶5d→4f⁷ transition in Eu²⁺ ion. The nanorod materials may find applications in red or green phosphors.3. MgAl₂O₄:Mn²⁺ hexagonal nanoplates have been synthesized via a simple two-step method. The Mg-Al-CO₃:Mn LDH precursor have been synthesized by homogeneous precipitation method with the hydrolyzation of urea. The synthesized MgAl₂O₄:Mn²⁺ nanoplates are single-crystal, with uneven surface and non uniform thickness. This is the result of thermal evolution of precursor as well as structure rearrangement and the treatment with hydrochloric acid. Photoluminescence spectrum of the MgAl₂O₄:Mn²⁺ nanoplate at the excitation of 390 nm shows a broad green emission band centered at 568 run, which is assigned to the ⁴T₁(⁴G)→⁶A-1(⁶S) transition of Mn²⁺ ion. The MgAl₂O₄:Mn²⁺ nanoplate is a promising candidate for efficient nanoscale optical material.4. Using the fluxing agent B₂O₃ as reactant, BN nanosheets-coated SrAl₂O₄:Eu²⁺ have been fabricated by a simple one-pot method. The BN nanosheets formed into a compact layer coating on the surface of SrAl₂O4:Eu²⁺ completely, which could obstruct H₂O molecule entering into the channels of SrAl₂O₄, and restrain SrAl₂O₄ from hydrolyzing effectively. The emission peak intensity for BN-coated phosphor is a little weaker than that of uncoated phosphor. We believe that this simple method reported here opens up many opportunities for the fabrication of other kinds of water-resistant aluminate phosphors.5. Lanthanum borate nanowires have been fabricated by CNTs template-confined growth method at 1100℃. The crystal structure and the composition of the nanowires have also been investigated. Carbon nanotubes play an important role in the growth process. The morphology of lanthanum borate nanowires depends on the shape of the carbon nanotubes at high reaction temperatures. This new one-dimensional rare earth orthoborate may find applications in useful host lattice for optical materials.