Combustion Synthesis Europium Ions (Eu～(2+)) Doped Alkaline Earth Aluminates Persistent Luminescence Phosphor And Their Optical Properties

Photoluminescent material with long persistent luminescence is a kind of energy storage material that can absorb both the ultraviolet (UV) and visible lights from the sunlight and gradually release the energy in the darkness at a certain wavelength. The photoluminescence at the violet–yellow visible region of divalent europium ions (Eu²⁺) doped alkaline earth aluminates MAl₂O₄:Eu²⁺ (M = Ca, Sr, Ba) phosphor have been widely studied because they have good luminescent properties, such as high initial luminescent, intensity, long lasting time, suitable emitting color and chemical stability, which resulted in an unexpectedly large field of applications, such as luminous paints in highway, airport, buildings and ceramics products.The solid-state reaction process has been used intensively for phosphor synthesis, but this process often results in poor homogeneity and requires high calcinating temperature. Furthermore, the grain size of phosphor powders prepared through solid-state reaction method is in several tens of micrometers. Phosphors of small particles must be obtained by grinding the larger phosphor particles. Those processes easily introduce additional defects and greatly reduce luminescence efficiency. With the development of scientific technologies on materials, several chemical synthesis techniques, such as co-precipitation, sol–gel, microwave and combustion synthesis methods have been applied to prepare the rare earth ions activation alkaline earth aluminate and/or its phosphors. All of these methods were conducted in liquid phases so that each component can be accurately controlled and uniformly mixed. The combustion process to prepare the precursor powders, however, is very facile and only takes a few minutes, which has been extensively applied to the preparation of various oxide materials. This synthesis technique makes use of the heat energy liberated by the redox exothermic reaction at a relative low igniting temperature between metal nitrates and urea or other fuels. Furthermore, the process is also safe, instantaneous and energy saving.In this dissertation, Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺, CaAl₂O₄:Eu²⁺,Nd³⁺ and SrAl₂O₄:Eu²⁺,Dy³⁺,Ho³⁺ phosphor with high brightness and long persistent luminescence was synthesized by combustion method. X-ray diffractometer (XRD), transmission electron microscope (TEM), luminescence spectrophotometer and brightness meter were used to analyze and measure the crystal structure, morphology, excitation and emission spectra, and long persistent decay curve of the phosphor, respectively, the luminescence mechanism was also discussed.The master work showed that:1. The Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor nanoparticles were synthesized at the first time by combustion synthesis processing, along with heating the precursor powder at 1300℃in a protective atmosphere of N₂. Analytical results showed that the nanometer phosphors have pure monoclinic Sr₄Al₁₄O₂₅ phase, with the average particles size in the range of 20–40 nm. Compared with the solid-state reaction method, the blue shifts of main peaks of emission of the nanometer phosphors occur and the particles size are tinier.2. The synthesis technology of Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ long persistent phosphor was optimization using the orthogonal design method. The test results indicate that by correct selection of the operating parameters the better Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ long persistent phosphor can be obtained through the combustion process.3. Eu²⁺, Nd³⁺ co-doped calcium aluminate persistent luminescence was prepared by the combustion method. The luminescent properties of CaAl₂O₄-based luminescent materials have been studied systematically.4. Eu²⁺,Dy³⁺,Ho³⁺co-doped strontium aluminate with high brightness and long persistent luminescence were prepared at the first time by the combustion method at 600℃. The decay time of the persistence indicated that the persistent luminescence phosphor of SrAl₂O₄:Eu²⁺,Dy³⁺,Ho³⁺ have better phosphorescence than the tradition phosphor of SrAl₂O₄:Eu²⁺,Dy³⁺.