Eu^(2+)掺杂A_(2)CaPO_(4)F(A=K,Rb)格位占据和发光性质的第一性原理研究

First-principles on Site Occupation and Luminescence Properties of Eu^(2+)-doped A_(2)CaPO_(4)F(A=K,Rb)

Eu^(2+)⁃激活A_(2)CaPO_(4)F(A=K,Rb)荧光粉因具有优异的发光性能而引起研究人员的重点关注。然而,Eu^(2+)掺杂格位占据和光谱指认及其光谱调控机制依然不甚清楚。本文采用密度泛函理论系统计算了Eu^(2+)占据不同晶体学格位时的缺陷形成能及光学跃迁能量,以此为基础对发射光谱进行指认。结果表明,K_(2)CaPO_(4)F∶Eu^(2+)位于660 nm附近和480 nm附近的发射峰虽然都来自Eu^(2+)占据在K格位,但二者的电荷补偿方式不同:前者两个配位F原子被O原子取代,同时与其中一个O原子近邻的K原子被Ca原子取代;后者只有一个配位F原子被O原子取代。Rb_(2)CaPO_(4)F∶Eu^(2+)位于480 nm附近的发射峰来自Eu^(2+)占据Rb格位,电荷补偿方式为:两个配位F原子被O原子取代,同时与两个O原子都相邻的K原子被Ca原子取代。此外,对Eu^(2+)占据格位的配位环境和电子结构进行分析,讨论了其与光谱发射峰位置之间的变化关系。本工作不仅诠释了实验现象,还可以为实验上进一步优化荧光粉发光性能提供理论参考。

Eu-activated ACaPOF(A=K,Rb)phosphors have attracted significant attention for theirsuperior luminescence properties.However,the site occupation,the associated spectral assignmentof dopant Eu,and hence the mechanism behind the site-regulated emission tuning,still remain elu-sive.Herein,we carried out systematic density functional theory calculations on defect formation en-ergies and optical transitions of Eusituated at different crystallographic sites with various localcharge compensations.It shows that,for KCaPOF∶Eu,the~660 nm emission is due to Eulocat-ed on the K site with charge compensation by two coordinating Osubstitutions plus one Canear oneof the two Odefects,while the~480 nm emission comes from Eulocated on the K site with chargecompensation by one coordinating Osubstitution.For RbCaPOF∶Eu,the~480 nm emission orig-inates from Eulocated at the Rb site with two coordinating Odefects plus one Canear both the Odefects.On this basis,we analyze Eulocal environments and electronic properties,and discusstheir relationship with the relative spectral shift from Euin KCaPOF∶Euto RbCaPOF.Our re-sults can not only assist in the understanding of experimental observations but also provide a theoretical basis for further performance optimization of the phosphors.