J. Rare Earths., 2021, 39(4), 386-389https://www.sciencedirect.com/science/article/abs/pii/S1002072120300053

As a promising narrow-band phosphor, SrLiAl₃N₄ has a seemingly ultra-small total crystal-field splitting of only 2400 cm⁻¹ with Ce³⁺ as dopant ions. This paper is devoted to unravel this anomalous phenomenon based on semi-quantitative crystal-field calculations. The results show that there may exist undetected excitation peaks immersed in the host excitation band, and the calibrated crystal-field splitting is 27000 cm⁻¹, comparable to those of other Ce³⁺ doped phosphors. In the end the effect of polyhedral deformation on energy level is briefly discussed.

J. Am. Ceram. Soc., 2019, 102(8), 4648-4658. https://ceramics.onlinelibrary.wiley.com/doi/abs/10.1111/jace.16337

Nitride phosphors of Ca_0.99−xSr_xAl_1.01Si_0.99N₃:0.01Ce³⁺ (0 ≤ x ≤ 0.9) were synthesized by conventional solid-state method. XRD data analysis shows that all samples are single phase with CaAlSiN₃-type structure. Under blue or near-ultraviolet (~400 nm) light excitation, the emission peak can be tuned largely from 615 to 568 nm by increasing Sr content, and the emission intensity is maximal at x = 0.8. With the Sr content increase, the emission band blue-shifts due to the decreased crystal field splitting and the reduced centroid shift; while the thermal luminescence quenching resistance is almost unchanged. The quenching temperature (T₅₀) is well above 500 K for all samples, which satisfies the requirement of commercial application. The quenching process is mainly attributed to the radiationless transitions by thermally activated crossover from the 5d excited state to 4f ground state in the configurational coordinate diagram. The luminescence properties show that the (Ca,Sr)AlSiN₃:Ce³⁺ phosphors are very promising for use in blue and near-ultraviolet light excited white-light-emitting diodes.

J. Phys. Chem. C., 2020, 124, 1, 870–873. https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.9b09322

The structure–property relationship is a hot research topic in both chemistry and material science. A structural descriptor has significant applications in machine learning and high-throughput screening for rapid estimations of material properties. In this work, we report a simple structural indicator to characterize the crystal-field splitting of Ce³⁺ ions in the garnet structure. The indicator is the interplanar distance of the octahedron, which is calculated as 2/√3 | x + y + z | · L, where L stands for the cell parameter and (x, y, z) are the oxygen coordinates in a specific form. The indicator value is correlated to the crystal-field splitting of Ce³⁺ in the lanthanide aluminum/gallium garnets and is able to reproduce the reverse garnet effect. By inspecting the polyhedral competition effect in the garnet structure, this indicator is found to be correlated to the tetragonal distortion of the dodecahedron, which determines the crystal-field splitting.

https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.9b00395

Herein, we provide a direct explanation for the reverse garnet effect based on polyhedron competition. On multisite substitution, the deformation of the dodecahedron which will accommodate Ce³⁺ meets suppression from a neighboring octahedron and tetrahedron. This makes the dodecahedral deformation nonisotropic. Further, it is found that the lowest 5d state of Ce³⁺ in garnet is closely related to the tetragonal distortion of the dodecahedron, which is characterized by a simplified cuboid model. Crystal-field calculations reveal how the edge-ratio of the cuboid affects energy levels. This model gives a satisfactory explanation for the reverse garnet effect and is helpful for seeking novel garnet-based luminescent materials.