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【答案】应助回帖
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爱哭的星星: 金币+100, 翻译EPI+1, ★★★★★最佳答案 2017-02-25 15:05:47
From the thermodynamic point of view, the activation energy of hexagonal phase NaYF4 is higher than that of the formation of cubic phase NaYF4, and the high temperature environment can provide enough energy to overcome the potential barrier of hexagonal NaYF4. Thus, increasing the temperature of the reaction can promote the transition of the NaYF4: Yb, Er nanoparticles from the cubic phase to the hexagonal phase.
From the kinetic point of view, the conversion from α-NaYF4 to β-NaYF4 is a cationic arrangement from disorder to orderly process, forming an ordered structure longer than the time required to form a disordered structure. Therefore, prolonging the reaction time can promote the transition of NaYF4: Yb, Er nanoparticles from cubic phase to hexagonal phase.
Although the hexagonal phase NaYF4 is thermodynamically stable, it is often obtained in the synthesis that the cubic phase of NaYF4. This is because the activation energy of the β-crystal form of NaYF4 crystals is higher than that of the formation of α crystal form. If NaYF4 does not provide enough energy to overcome the potential barrier of β crystal when crystallized, NaYF4 is very easy to crystallize Unstable α crystal form. Under certain conditions, the two crystal forms of NaYF4 can be converted to each other. The transition from α-crystal to β-crystal form of NaYF4 usually takes place in a more intense environment, such as higher temperatures or longer heating reactions. |
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