Unraveling the Photoluminescent Properties of Sb-Doped Cd-Based Inorganic Halides: A First-Principles Study

Sb-doped Cd-based inorganic halides, with varying connections of CdCl6 octahedra ranging from 0D to 3D, exhibit a variety of photoluminescent properties. Single-band emission is observed in Sb-doped Rb4CdCl6 (0D) and Cs2CdCl4 (2D), while dual-band emission is seen in Sb-doped RbCdCl3 (1D) and CsCdCl3 (3D). Density-functional-based first-principles calculations were conducted. The results reveal that cation vacancies, acting as charge compensators, influence the luminescence properties of dopant centers. In CsCdCl3, the local cation vacancy VCd″ for Sb3+ at the Cd2+ site ([Sb□Cl9]6–) significantly modifies the photoluminescence property, accounting for the observed dual-band emission alongside the nonlocal compensation case. This effect is insignificant in Sb-doped Rb4CdCl6, RbCdCl3, and Cs2CdCl4, due to the large distances or high formation energies of Cd vacancies in these hosts. However, in Sb-doped RbCdCl3, two different potential energy minima, one that involves typical structure relaxation and the other that is off-center, lead to the observed dual-band emission. Furthermore, the shift of the charge transition level illustrates the different temperature dependences of the dual-band emission caused by the charge-compensating point defects. These insights not only enhance our understanding of luminescent materials based on halides containing ns2 dopants but also provide valuable guidance for the design and optimization of luminescent materials

A Theoretical Study on the Structural and Energy Spectral Properties of Ce³⁺ Ions Doped in Various Fluoride Compounds

Geometry optimization and wave function-based complete-active-space self-consistent field-embedded cluster calculations have been performed for a series of Ce³⁺-doped fluoride compounds (CaF₂, YF₃, LaF₃, KMgF₃, LiYF₄, K₂YF₅, and KY₃F₁₀) to investigate local coordination structures, crystal field parameters, and 5d¹ energy-level structures of doping Ce³⁺ ions. The crystal-field parameters of Ce³⁺ are extracted from the calculated energies and wave functions. The calculated crystal-field parameters and 5d¹ energy-level structures show excellent consistency with the experimental results. Our calculations show that the onset of 4f → 5d absorption, which is important in phosphors and scintillators, can be well-predicted. Apart from that, the distortion of local structure due to doping, the wave functions, and the crystal-field parameters of 4f¹ and 5d¹ states of Ce³⁺ in the hosts can be obtained. Those can seldom be obtained by fitting empirical crystal-field Hamiltonian to experimental data but are required by some detailed theoretical analysis, such as the calculation of transition intensities and hyperfine splittings. The obtained crystal-field parameters of Ce³⁺ may also be useful for other lanthanide ions in the same hosts

First-Principles Study on Structural, Electronic, and Spectroscopic Properties of γ‑Ca₂SiO₄:Ce³⁺ Phosphors

In the present work, geometric structures, electronic properties, and 4f → 5d transitions of γ-Ca₂SiO₄:Ce³⁺ phosphors have been investigated by using first-principles calculations. Four categories of typical substitutions (i.e., the doping of the Ce³⁺ without the neighboring dopants/defects and with the neighboring V_O^••, Al_Si′, and V_Ca″) are taken into account to simulate local environments of the Ce³⁺ located at two crystallographically different calcium sites in the γ-Ca₂SiO₄. Density functional theory (DFT) geometry optimization calculations are first performed on the constructed supercells to obtain the information about the local structures and preferred sites for the Ce³⁺. On the basis of the optimized crystal structures, the electronic properties of γ-Ca₂SiO₄:Ce³⁺ phosphors are calculated with the Heyd–Scuseria–Ernzerhof screened hybrid functional, and the energies and relative oscillator strengths of the 4f → 5d transitions of the Ce³⁺ are derived from the <i>ab initio</i> embedded cluster calculations at the CASSCF/CASPT2/RASSI-SO level. A satisfactory agreement with the available experimental results is thus achieved. Moreover, the relationships between the dopants/defects and the electronic as well as spectroscopic properties of γ-Ca₂SiO₄:Ce³⁺ phosphors have been explored. Such information is vital, not least for the design of Ce³⁺-based phosphors for the white light-emitting diodes (<i>w</i>-LEDs) with excellent performance

Identifying the Emission Centers and Probing the Mechanism for Highly Efficient and Thermally Stable Luminescence in the La₃Si₆N₁₁:Ce³⁺ Phosphor

Nitride La₃Si₆N₁₁:Ce³⁺ is an important commercial phosphor for high-power white light-emitting diodes due to its strong resistance toward thermal quenching and sufficient emission efficiency. However, the underlying mechanisms of this high performance is still a mystery. Also, the emission properties of Ce³⁺ in two kinds of crystallographic sites are currently in dispute. Here, we confirmed the yellow emission ascribed to Ce_La(2) luminescence center and proposed a blue emission owning to Ce_La(1) luminescence center through both theoretical and experimental methods. Particularly, we find an unusual efficient and fast energy transfer from Ce_La(1) to Ce_La(2) due to a large spectral overlap between the emission of Ce_La(1) and the absorption of Ce_La(2), and efficient electron transfer from defects to 5d orbital at high temperature, which shows high relevance to the highly efficient yellow emission and thermal stability of this material. This study presents a full and new understanding toward this special phosphor and provides useful insights into designing highly efficient and thermally stable luminescent materials for future lighting