The Synthesis Of Aluminate (Silicate) Materials By Molten Salt Process And Their Photoluminescence

Photoluminescence materials, used widely in many fields, consist of fluorescent materials for lamp, long-afterglow materials, multiphoton materials. For that, research on photoluminescence materials becomes more hot and important in the 21st century of the future. Presently, many disadvantages exist in the approaches for preparing host materials, such as high prepared temperature, complicated process and environmental pollution for using many organic materials. Meanwhile, many host materials show poor thermal and chemical stability, bad chemical compatibility and water resistance. The limitation, either in the preparing approaches or for the host materials, are all retarding their wide applications.Molten salt synthesis, possesses low calcining temperature, simple process, uniform particle, comparing to traditional solid-state reaction, sol-gel synthesis, hydrothermal(solvothermal) synthesis, etc. Alkaline earth metal silicate and alkali metal aluminate have good thermal and chemical stability, excellent chemical compatibility and water resistance. Therefore, this thesis aimed to improve the synthesis methods, together with the research on preparation ofα-Sr₂SiO₄:Eu³⁺ andα-LiAlO₂:Eu³⁺ red photoluminescence materials by molten salt method. The formation and photoluminescence mechanisms were also investigated during the discussion of many factors in the synthesis process. Details are as follows:1. Laser host material YAlO₃ (YAP) was synthesized successfully by molten salt method assisted by an electrochemical process, ie. YAP precursor was prepared by an electrochemical method at room temperature, followed by calcining it at a temperature of not exceeding 400 oC for 8 h using LiNO₃ as the molten salt medium. XRD analysis and TEM observation show that well-crystallized YAP powders can be obtained at 400 oC for a holding time of 8 h with 1:16 ratio of YAP precursor to LiNO₃ by weight. The process decreased the calcining temperature of YAP greatly, meanwhile provided a reference to synthesize Eu³⁺ doped LiAlO₂ red photoluminescence materials by molten salt synthesis.2.α-Sr₂SiO₄:Eu³⁺ red photoluminescence materials were prepared by molten salt process, ie. Sr(NO₃)₂,Na₂SiO₃·9H₂O,Eu₂O₃ were used as the starting material, followed by calcining it at a temperature of not exceeding 900 oC for 8h. During the whole procedure, Sr(NO₃)₂ (Melting point 570 oC.) performed as a molten salt and a reactant. PL analysis shows that the photoluminescence performance ofα-Sr₂SiO₄:Eu³⁺ gets improved as the increase of Eu³⁺ loadings within a certain range and the best factors were as follows: The calcining temperature: 900 oC, Eu³⁺ loadings: 3mol%. 3.α-LiAlO₂ : Eu³⁺ red photoluminescence materials were prepared by a precipitation-molten salt method, ie. The precursor containing Eu³⁺,Li+,Al3+ were synthesized by a precipitation process, followed by calcining it at a temperature of not exceeding 500℃for 8 h. XRD and SEM results reveals that the existence of Eu³⁺ can stabilizeα-LiAlO₂ matrix to form a hexagonal solid solution, while the addition of LiNO₃ in calcining process can greatly lower their formation temperature and favor their crystallization. Theα-LiAlO₂:Eu³⁺ solid solutions exhibit improved PL property, and their PL intensity increases with Eu³⁺ loadings. It can be concluded thatα-LiAlO₂:0.05Eu³⁺ with a good photoluminescence property can be obtained at 500℃by a 1:8 weight ratio of precursor to LiNO₃ for 8h.