(A) high-temperature solid-state reaction method
This method is the most primitive method to prepare rare earth tricolor phosphor. Taking red phosphor (YEu)O3 in rare earth tricolor phosphor as an example, the preparation process of this method is as follows: Y2O3 and Eu2O3(99.99% or above) are weighed according to a certain stoichiometric ratio, added with quantitative flux, and evenly mixed at 1300- 1500? C, burning for about 2h, taking out, grinding and washing. This method is simple to operate, but the particle size is large, which will cause component segregation and reduce the luminous efficiency. If the sintering temperature is too high, it will be seriously sintered, which will destroy the lattice position of the activator in the final grinding, thus reducing the luminous efficiency.
(2) preparing a precursor by a * * * precipitation method
After discovering the shortcomings of high-temperature solid-state reaction, people have been exploring a new method to try to overcome the shortcomings of high-temperature solid-state reaction. It is found that synthesizing phosphor in solution will make the composition of the product uniform. The method is as follows: (Take red phosphor as an example) Take a certain proportion of Y2O3 and Eu2O3 (above 99.99%) and dissolve them with HNO3 or HCl to make mixed rare earth acid solution, and then react with oxalic acid until it is completely dried. Other methods are the same as the method (1). The product prepared by this method has relatively uniform composition and less segregation, but the particle size is not easy to control, and the process is slightly more complicated than the first method.
Both of the above two methods make the commonly used products also form industrial production. Although both methods have shortcomings, the products prepared by these two methods have great advantages over the products synthesized by other methods in terms of luminous performance.
(3) Sol-gel method
There are two methods to prepare fluorescent materials by sol-gel method: one is to mix rare earth ion activator into the initial reaction solution to form gel, or to soak the prepared gel in a solution containing rare earth activator. The prepared gel is processed into powder at a certain temperature. This method is simple and easy to master, and the prepared products are uniform and small in particle size, but it takes a long time and has a small throughput. The cost is high and the luminous intensity needs to be improved.
(4) Combustion method
The method mainly includes the following steps: adding a certain amount of organic matter in the preparation process, and reducing the final combustion temperature by releasing a large amount of heat when the organic matter burns; At the same time, a large amount of gas produced during the combustion of organic matter can reduce the agglomeration of products, thus obtaining products with smaller particles. The product synthesized by this method has small particles, uniform components, low sample synthesis temperature and reduced energy consumption. However, this method has a small amount of treatment each time, and the cost will increase after adding organic matter.
In addition to the two methods mentioned above, it is also reported that fluorescent materials can be prepared by hydrothermal method and freeze-drying method. The phosphor synthesized by these methods mainly solves the problem of large particle size, but the production cost has not been improved. Due to the limitation of methods, the four methods introduced later can not be applied to actual production at present.