Theoretical and Structural Study of Axial Symmetry Ce3+ Centers in the BaWO4 Single Crystal Doped with Cerium and Codoped with Sodium Ions

The spin-Hamiltonian parameters g-factors (g|| and g⟂) of the Ce³⁺ paramagnetic centers in BaWO₄: Ce and BaWO₄: Ce, Na single crystals with axial symmetry are investigated using the superposition model (SPM) via complete diagonalization procedure of energy matrix (CDM method). The calculated g-factors are in reasonable agreement with the experimental values. The fitted intrinsic parameters are comparable with data from other publications for rare-earth paramagnetic centers in a similar environment. The angular distortions of the cerium dodecahedron [CeO₈] are also studied. Structural analysis of paramagnetic centers with axial symmetry through the postulated cerium barium tetrahedron [CeBa₄] connected via oxygens bridges was carried out. The mechanism of the charge compensation and the role of the second dopant (Na⁺) is also discussed.

Tunable Luminescence and Energy Transfer of Sr3B2O6:Ce3+, Sm3+ Phosphors with Potential Anti-Counterfeiting Applications

Sm³⁺ and Ce³⁺ singly doped and Sm³⁺ and Ce³⁺ co-doped Sr₃B₂O₆ phosphors are prepared via a high-temperature solid-state reaction method. The crystal structure and phase purity are characterized by X-ray diffraction (XRD) analyses. The Sm³⁺-doped sample displays an emission in the orange-red region, with the strongest emission line at about 648 nm and possessing a good luminescence thermal stability between 78 and 500 K. With the increase in the Sm³⁺ content, the concentration quenching is observed due to the cross-relaxation (CR) processes among the Sm³⁺ ions. Upon 340 nm excitation, the Ce³⁺-doped phosphor presents a broad emission band in the blue region with a maximum at about 420 nm, which overlaps well with the ⁶H_5/2 → ⁶P_3/2 excitation line of Sm³⁺ and implies the possible energy transfer from Ce³⁺ to Sm³⁺. The spectral and decay measurements of the Ce³⁺ and Sm³⁺ co-doped samples are conducted and the Inokuti-Hirayama (I-H) model is adopted to analyze the luminescence decay dynamics of the donor Ce³⁺. Owing to the evident sensitization of the Sm³⁺ by the Ce³⁺ ions, the co-doped samples exhibit color variation under different wavelength excitations, endowing them with potential applications in optical anti-counterfeiting.

Multiobjective Machine Learning-Assisted Discovery of a Novel Cyan-Green Garnet: Ce Phosphors with Excellent Thermal Stability

Ce-doped garnet phosphors play an important role in the white light-emitting diode (LED) family. In the past years, a lot of trial-and-error experiments guided by experience to discover phosphors suitable for white LEDs have been presented. The working temperature of phosphors may reach 200 °C in white LEDs, and so, the exploration of phosphors with excellent thermal stability at the desired wavelength continues to be a challenge. In the present study, to discover novel cyan-green garnet:Ce phosphors, wavelength and thermal stability machine learning models were built by constructing reasonable features. Among the 171,636 compounds with garnet structures predicted by our models, 25 samples were selected for preparation and characterization by multiobjective optimization based on active learning. Lu_1.5Sr_1.5Al_3.5Si_1.5O₁₂:Ce performed the best with excellent thermal stability (≥60% emission intensity was retained at 640 K) and exhibited emission peaks of about 505 nm, and it is a very promising phosphor for future applications, especially in high-temperature operating environments.

Energy transfer induced white-light-emitting phosphor by co-doping Ce3+ , Tb3+ and Mn2+ into the single Ba9 Lu2 Si6 O24 host

In the Ba₉ Lu₂ Si₆ O₂₄ (BLS) host, Ce³⁺ shows cyan emissions peaking at 490 nm under 400 nm excitations. BLS:Tb³⁺ only can be effectively excited by 254 nm light and gives rise to green emissions at 553 nm. However, both the cyan and green emissions can be obtained in BLS:Ce³⁺ ,Tb³⁺ under 400 nm excitations due to effective energy transfers from Ce³⁺ to Tb³⁺ . BLS:Mn²⁺ shows red emissions peaking at 610 nm under 414 nm excitations. By co-doping Ce³⁺ , Tb³⁺ and Mn²⁺ , tunable full-color emissions were obtained. The BLS:0.3Ce³⁺ ,0.6Tb³⁺ ,0.15Mn²⁺ single phosphor exhibits a white light with a high color rendering index of 85 and a correlated color temperature of 5480 K under 400 nm excitation.

Tailoring Trap Depth and Emission Wavelength in Y3Al5- xGa xO12:Ce3+,V3+ Phosphor-in-Glass Films for Optical Information Storage

Deep-trap persistent luminescent materials, due to their exceptional ability of energy storage and controllable photon release under external stimulation, have attracted considerable attention in the field of optical information storage. Currently, the lack of suitable materials is still the bottleneck that restrains their practical applications. Herein, we successfully synthesized a series of deep-trap persistent luminescent materials Y₃Al_{5- x}Ga _xO₁₂:Ce³⁺,V³⁺ ( x = 0-3) with a garnet structure and developed novel phosphor-in-glass (PiG) films containing these phosphors. The synthesized PiG films exhibited sufficiently deep traps, narrow trap depth distributions, high trap density, high quantum efficiency, and excellent chemical stability, which solved the problem of chemical stability at high temperatures in the reported phosphor-in-silicone films. Moreover, the trap depth in the phosphors and PiG films could be tailored from 1.2 to 1.6 eV, thanks to the bandgap engineering effect, and the emission color was simultaneously changed from green to yellow due to the variation of crystal field strength. Image information was recorded on the PiG films by using a 450 nm blue-light laser in a laser direct writing mode and the recorded information was retrieved under high-temperature thermal stimulation or photostimulation. The Y₃Al_{5- x}Ga _xO₁₂:Ce³⁺,V³⁺ PiG films as presented in this work are very promising in the applications of multidimensional and rewritable optical information storage.

Formation of Deep Electron Traps by Yb3+ Codoping Leads to Super-Long Persistent Luminescence in Ce3+-Doped Yttrium Aluminum Gallium Garnet Phosphors

The Y₃Al₂Ga₃O₁₂:Ce³⁺-Cr³⁺ compound is one of the brightest persistent phosphors, but its persistent luminescence duration is not so long because of the relatively shallow Cr³⁺ electron trap. To compare the vacuum referred binding energy of the electron trapping state by Cr³⁺ and lanthanide ions, we selected Yb³⁺ as a deeper electron trapping center. The Y₃Al₂Ga₃O₁₂:Ce³⁺-Yb³⁺ phosphors show Ce³⁺:5d → 4f green persistent luminescence after blue light excitation. The formation of Yb²⁺ was confirmed by the increased intensity of absorption due to Yb²⁺:4f-5d at 585 nm during the charging process. This result indicates that the Yb³⁺ ions act as electron traps by capturing an electron. From the thermoluminescence glow curves, it was found that the Yb³⁺ trap makes a much deeper electron trap with a 1.01 eV depth than the Cr³⁺ electron trap with a 0.81 eV depth. This deeper Yb³⁺ trap provides a much slower detrapping rate of filled electron traps than the Cr³⁺-codoped persistent phosphor. In addition, by preparing transparent ceramics and optimizing Ce³⁺ and Yb³⁺ concentrations, the Y₃Al₂Ga₃O₁₂:Ce³⁺(0.2%)-Yb³⁺(0.1%) as-made transparent ceramic phosphor showed super-long persistent luminescence for over 138.8 h after blue light charging.

Comparison of luminescence property of gamma-ray irradiated Tb3+ -doped and Ce3+ co-doped potassium halide single crystals

Single crystals of KCl and KBr singly and doubly doped with Tb³⁺ and Ce³⁺ , respectively, were successfully grown using the Bridgeman technique. This work reports the comparative luminescence behavior and optical absorption characterization of non-irradiated and γ-ray-irradiated single crystals of these materials. The existing defect and the defect created by γ-ray irradiation were monitored by optical absorption spectra. The excitation and emission spectra of these materials were measured at room temperature with a spectrofluorometer and the pertaining results were compared. The F-band comparison was made when bleached with F-light for 2 mins. The trap-level changes in KCl and KBr when it is singly and doubly doped enabled us to draw conclusions on the nature of the defect and on the recombination processes involved.