4 research outputs found
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 Ce<sup>3+</sup> 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 Ce<sup>3+</sup>-doped fluoride compounds (CaF<sub>2</sub>, YF<sub>3</sub>, LaF<sub>3</sub>, KMgF<sub>3</sub>, LiYF<sub>4</sub>, K<sub>2</sub>YF<sub>5</sub>, and KY<sub>3</sub>F<sub>10</sub>) to investigate local coordination structures, crystal field parameters,
and 5d<sup>1</sup> energy-level structures of doping Ce<sup>3+</sup> ions. The crystal-field parameters of Ce<sup>3+</sup> are extracted
from the calculated energies and wave functions. The calculated crystal-field
parameters and 5d<sup>1</sup> 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 4f<sup>1</sup> and 5d<sup>1</sup> states of Ce<sup>3+</sup> 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 Ce<sup>3+</sup> may also be useful for other lanthanide
ions in the same hosts
First-Principles Study on Structural, Electronic, and Spectroscopic Properties of γ‑Ca<sub>2</sub>SiO<sub>4</sub>:Ce<sup>3+</sup> Phosphors
In
the present work, geometric structures, electronic properties,
and 4f → 5d transitions of γ-Ca<sub>2</sub>SiO<sub>4</sub>:Ce<sup>3+</sup> phosphors have been investigated by using first-principles
calculations. Four categories of typical substitutions (i.e., the
doping of the Ce<sup>3+</sup> without the neighboring dopants/defects
and with the neighboring V<sub>O</sub><sup>••</sup>,
Al<sub>Si</sub>′, and V<sub>Ca</sub>″) are taken into
account to simulate local environments of the Ce<sup>3+</sup> located
at two crystallographically different calcium sites in the γ-Ca<sub>2</sub>SiO<sub>4</sub>. 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 Ce<sup>3+</sup>. On the basis of the optimized crystal
structures, the electronic properties of γ-Ca<sub>2</sub>SiO<sub>4</sub>:Ce<sup>3+</sup> 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 Ce<sup>3+</sup> 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-Ca<sub>2</sub>SiO<sub>4</sub>:Ce<sup>3+</sup> phosphors have been explored. Such information
is vital, not least for the design of Ce<sup>3+</sup>-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 La<sub>3</sub>Si<sub>6</sub>N<sub>11</sub>:Ce<sup>3+</sup> Phosphor
Nitride
La<sub>3</sub>Si<sub>6</sub>N<sub>11</sub>:Ce<sup>3+</sup> 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 Ce<sup>3+</sup> in two kinds of crystallographic sites are currently in
dispute. Here, we confirmed the yellow emission ascribed to Ce<sub>La(2)</sub> luminescence center and proposed a blue emission owning
to Ce<sub>La(1)</sub> luminescence center through both theoretical
and experimental methods. Particularly, we find an unusual efficient
and fast energy transfer from Ce<sub>La(1)</sub> to Ce<sub>La(2)</sub> due to a large spectral overlap between the emission of Ce<sub>La(1)</sub> and the absorption of Ce<sub>La(2)</sub>, 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