Wen Jun, Wang Yan, Jiang Guisheng, Zhong Jiyou, Chu Jimin, Xia Qiangsheng, Zhang Qingping, Ning Lixin, Duan Chang-Kui, Yin Min
School of Physics and Electronic Engineering, Anqing Normal University, Anqing 246133, China.
The Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Normal University, Wuhu 241000, China.
Inorg Chem. 2020 Apr 6;59(7):5170-5181. doi: 10.1021/acs.inorgchem.0c00406. Epub 2020 Mar 20.
The origin of the self-activated luminescence in the apatite-type M(PO)X (MPOX; M = Sr or Ba; X = Cl or Br) samples and the spectral assignment for cerium-doped Sr(PO)Cl (SPOC) phosphors are determined from first-principles methods combined with hybrid density functional theory (DFT) calculations, using the standard PBE0 hybrid functional, with wave function-based embedded-cluster calculations (at the CASSCF/CASPT2/RASSI-SO level). Electronic structure calculations are performed in order to accurately derive the band gaps of the hosts, the locations of impurity states in the energy bands that are caused by native defects and doped Ce ions, and the charge-compensation mechanisms of aliovalent doping. The calculations of defect formation energies under O-poor conditions demonstrate that the native defects are easily generated in the undoped MPOX samples prepared under reducing atmospheres, from which thermodynamic and optical transition energy levels, as well as the corresponding energies, are derived in order to interpret the luminescence mechanisms of the undoped MPOX as previously reported. Our calculations reveal that the self-activated luminescence is mainly attributed to the optical transitions of the excitons bound to the oxygen vacancies (V), along with their transformation of the charge states 0 ↔ 1+. Furthermore, the eight excitation bands observed in the synchrotron radiation excitation spectra of SPOC: Ce, Na phosphors are successfully assigned according to the calculated energies and relative oscillator strengths of the 4f → 5d transitions for the Ce ions at both the Sr(1) and Sr(2) sites in the host. It is hoped that the feasible first-principles approaches in this work are applied in order to explore the origins of the luminescence in undoped and lanthanide-doped phosphors, complementing the experiments from the perspective of chemical compositions and the microstructures of materials.
通过结合混合密度泛函理论（DFT）计算的第一性原理方法，使用标准的PBE0混合泛函，并基于波函数的嵌入簇计算（在CASSCF/CASPT2/RASSI-SO水平），确定了磷灰石型M(PO)X（MPOX；M = Sr或Ba；X = Cl或Br）样品中自激活发光的起源以及铈掺杂的Sr(PO)Cl（SPOC）荧光粉的光谱归属。进行电子结构计算，以准确推导主体的带隙、由本征缺陷和掺杂Ce离子引起的杂质态在能带中的位置以及异价掺杂的电荷补偿机制。在贫氧条件下缺陷形成能的计算表明，在还原气氛中制备的未掺杂MPOX样品中容易产生本征缺陷，从中推导了热力学和光学跃迁能级以及相应的能量，以解释先前报道的未掺杂MPOX的发光机制。我们的计算表明，自激活发光主要归因于与氧空位（V）结合的激子的光学跃迁，以及它们电荷态0 ↔ 1+的转变。此外，根据主体中Sr(1)和Sr(2)位点上Ce离子的4f → 5d跃迁的计算能量和相对振子强度，成功地确定了SPOC:Ce,Na荧光粉同步辐射激发光谱中观察到的八个激发带。希望应用这项工作中可行的第一性原理方法，从材料的化学成分和微观结构的角度补充实验，探索未掺杂和镧系掺杂荧光粉发光的起源。
