5d Level Of Ce3 Research Articles

First-principles study of the Li(Y/Lu)SiO4:Ce3+,Sm3+ storage phosphor

First-principles calculations are carried out to study the native point defects and dopants (Ce3+, Sm3+) in Li(Y/Lu)SiO4 for revealing the mechanism of the optical excitation energy storage properties. The calculated excitation and emission energies, the Stokes shifts as well as the positions of 4f and 5d levels of Ce3+ relative to host band edges show great consistent with the experimental results. The calculated formation energies reveal that the Li vacancies (VLi) and the antisite defects LiY and YLi (or LiLu and LuLi) are always much more energetically favorable than Y or Lu vacancies (VY or VLu) and O vacancies (VO) in Li(Y/Lu)SiO4 under reductive atmospheres. Moreover, according to the calculated charge transition levels of the native point defects and the dopants, the antisite defects YLi (or LuLi) and the dopants Sm3+ (SmY or SmLu) are deemed as electron traps that provide suitable charge transition levels for information storage in Li(Y/Lu)SiO4. Based on our calculations, a mechanism diagram of charge carrier storage and recombination during irradiation and thermal or optical readout is constructed for the storage phosphors Li(Y/Lu)SiO4:Ce3+,Sm3+.

Temperature dependence of 4fn−15d1→4fn luminescence of Ce3+ and Pr3+ ions in Sr2GeO4 host

Photoluminescence of Ce3+- and Pr3+-activated Sr2GeO4 powders was measured between 17 and 600 K. For both ions strong 4fn−15dn→4fn (d-f) emission is observed at low temperatures, around 410 nm (Ce3+) and 280 nm (Pr3+). The Ce3+ d-f emission quenches starting at 150 K and disappearing completely just above room temperature. Pr3+ d-f luminescence shows an onset of quenching also around 150 K and disappears completely between 250 and 300 K. For Pr3+ quenching of the d-f emission was connected with an increasing intensity of the 3P0 luminescence at first and 1D2 emission at even higher temperatures. Both these 4fn→4fn emissions were observed up to 600 K. Based on the similar quenching temperatures, thermally stimulated photoionization of the 5d electrons from 5d level of Ce3+ or Pr3+ to the conduction band is proposed as the most probable mechanism for quenching of the d-f emissions.

Near-infrared Quantum Cutting for Solar Cells in Ce3+-Yb3+ Co-Doped CaF2 Nanoparticles.

A series of Ce3+-Yb3+ co-doped CaF2 nanoparticles were prepared by a hydrothermal synthesis method. The structure, morphology, photoluminescence properties, and fluorescence dynamics were studied systemically. Under the excitation of the 5d level of Ce3+, an efficient energy transfer from Ce3+ to Yb3+ occurred, and the efficient near-infrared emission at 900-1050 nm matching to the energy of Si band gap of Si-based solar cells was observed. The lifetime of Ce3+ decreased, and the inner quantum efficiency increased with increasing Yb3+ concentration. The quantum efficiency dependent on Yb3+ concentration was calculated, and the maximum efficiency approached 186%. As a down-conversion luminescent convertor, this kind of material can be used in front of Si-based solar cells to reduce thermalization loss and enhance conversion efficiency of solar cells.

Preparation of the BaF<sub>2</sub>: Ce<sup>3+</sup>, Yb<sup>3+</sup> Nanoparticles and near Infrared Luminescent Properties

The BaF2: Ce3+, Yb3+ nanoparticles doped with different concentration were prepared by a hydrothermal method. The structure,morphology and photoluminescence properties were studied. In BaF2: Ce3+, Yb3+ nanoparticles, a strong near infrared emissionat 900 – 1050 nm matching to energy of Si band gap of Si-based solar cells was observed under the excitation of 5d level of Ce3+. As a downconversion luminescent convertor, the kinds of materials have potential to be applied in front of Si-based solar cells to reduce thermalization loss and enhance conversion efficiency of solar cells.

Preparation and Photoluminescent Properties of Ce<sup>3+</sup>, Yb<sup>3+</sup> Co-Doped YF<sub>3</sub> Nanophosphors for Solar Cells

An efficient near-infrared (NIR) quantum cutting (QC) nanophospors with Ce3+, Yb3+ co-doped in YF3 had been prepared by hydrothermal method and characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), photoluminescence spectra and decay dynamics. The obtained nanorods were uniform and monodisperse. Under the excitation of 5d level of Ce3+, an intense NIR emission at 900 1100 nm was observed which match to the energy of Si band gap of Si - based solar cells. In the Ce3+, Yb3+ codoped YF3, the lifetime of Ce3+ decreases and the quantum efficiency (QE) increases with increasing Yb3+ concentration.

Host effects on the optically active 4f and 5d levels of Ce3+ in garnets

When Ce(3+) is doped in a garnet, it substitutes for some cations. The effect of the substitution on the optically active 4f and 5d levels of Ce(3+) can be analyzed in terms of an undistorted substitution followed by a structural relaxation, but, whereas the contribution of the undistorted substitution can be predicted/calculated using the crystallographic structure of the pure garnet, which is at hand, that of the structural relaxation demands the detailed local structure around the Ce(3+) impurity, which is hard to know. Hence the importance of knowing the role of the undistorted substitution. What we study in this paper is the role of the unrelaxed host effects on the 4f and 5d levels of Ce(3+)-doped garnets (i.e. the interactions between Ce and the second and more distant neighbors). When they are added to the (previously studied) unrelaxed first-neighbor effects, they give the contributions of the undistorted substitutions. We performed spin-orbit coupling, relativistic, embedded cluster, wave function based ab initio calculations on the (CeO8)(13-) cluster under the effects of the embedding potentials of 21 selected garnets of Si, Al, and Ga, which have been obtained in this work, using experimental unrelaxed structures of the pure garnets. The calculations reveal that the unrelaxed host effect: (1) produces a red shift of the first 4f → 5d transition and (2) is an important contribution to this transition which plays a very important role in differentiating the values it has in different garnet families. The unrelaxed host effect is found to be responsible for the low value of the first 4f → 5d transition in Ce(3+)-doped Lu2CaMg2Si3O12. It is analyzed in terms of 5d and 4f centroid energy contributions and crystal field splitting contributions in the 21 doped garnets. The effect on the splittings of the 4f and 5d levels is also discussed. The undistorted host approximation is found to give reasonable comparison with experiments, so that it represents a relatively fast way to provide reliable ab initio information on the 4f and 5d levels of Ce(3+) in garnets.

Effects of scandium substitution on the crystal structure and luminescence properties of LuBO3: Ce3+

The calcite phase of LuBO3 and ScBO3 polycrystalline powders were synthesized by solid state reaction method, and the Lu1−xScxBO3:Ce (x=0.2, 0.5, 0.7) single crystals were grown by the Czochralski method. A large composition deviation between the initial polycrystalline powders and final single crystal was confirmed by electron probe micro-analysis. Raman spectroscopy revealed that moderate lattice disorder was induced by scandium substitution. However, based on the single crystal X-ray study, we finally concluded that the crystal structure of lutetium scandium orthoborate still crystallized in the rhombohedral system belonging to R3−c. Furthermore, the relationship between the energies of the five 5d levels of Ce3+ and the crystalline environment was revealed. The total redshift, total crystal field splitting, and centroid shift of Lu1−xScxBO3:Ce3+ were calculated based on their VUV excitation spectra. The variations trend of these observed spectroscopic parameters was in accordance with the predicted ones.

Near-Infrared Quantum Cutting Nanophosphors for Solar Cells

An efficient near-infrared (NIR) quantum cutting (QC) nanophospors with Ce3+, Yb3+ codoped in CaF2 had been synthesized by hydrothermal method and characterized by X-ray powder diffraction, scanning electron microscope, transmission electron microscopy, photoluminescence spectra and decay dynamics. The nanoparticles were uniform and monodisperse. Under the excitation of 5d level of Ce3+, an intense NIR emission at 900-1050nm was observed which match to the energy of Si band gap of Si - based solar cells. In the Ce3+, Yb3+ codoped CaF2, the lifetime of Ce3+ decreases Superscript textand the quantum efficiency (QE) increases with increasing Yb3+ concentration.

Near Infrared Quantum Cutting for Solar Cells in CeF<sub>3</sub>:Yb<sup>3</sup><sup>+</sup> Nanophosphors

The CeF3 nanophosphors with Yb3+ concentrations from 0 to 8% had been prepared by hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Their photoluminescence properties including excitation spectra, Uv-visibe and near infrared (NIR) emission spectra and fluorescence dynamics were studied. In the CeF3: Yb3+ nanophosphors an intensity infrared emission originated from Yb3+2F5/2 - 2F7/2 transition at 900-1050 nm matching to the energy of Si band gap of Si-based solar cells was observed under the excitation of 5d level of Ce3+. The lifetime of Ce3+ decreases and the quantum efficiency (QE) increases with increasing Yb3+ concentration.

Exchange and crystal field effects on the 4fn−15d levels ofTb3+

The levels of the 4fn−15d configuration of Ce3+(n = 1), Pr3+(n = 2), andTb3+(n = 8)in compounds are compared with each other. A model is presented that, by meansof energy shift operations performed on the five 5d levels of Ce3+,reproduces the energies of those for Pr3+ and Tb3+. UsingTb3+data, two main sources of deviations from the shift model areidentified. One is related to the size difference between Tb3+ andCe3+which affects the lattice relaxation and the crystal field splitting ofthe 5d configuration. The other is related to the isotropic exchangeinteraction between the 5d electron spin and the total spin of the 4f7 electrons inTb3+.The exchange splitting is about 1 eV in fluorides, sulfates, andphosphates. In oxides with less strongly bonded oxygen 2p electrons,the exchange splitting decreases to 0.6 eV. The effects of the twodeviations on the predictability of the 4fn−15d energy levels ofTb3+and other lanthanides are discussed.

4f–5d spectroscopy of Ce3+ in CaBPO5, LiCaPO4 and Li2CaSiO4

The properties of Ce3+ in CaBPO5, LiCaPO4 and Li2CaSiO4 have been studied inthe 100–400 nm wavelength region with time resolved spectroscopy attemperatures between 10 and 300 K. Emphasis is on the relationship betweenthe energies of the five 5d levels of Ce3+ and the crystalline environment.Good agreement between predicted and observed average energy of the 5dconfiguration is demonstrated. In addition values for the bandgap of the hostmaterials, Stokes shifts and luminescence decay time data are presented.

Band structure calculations of cerium activated inorganic scintillators

Trivalent cerium has been used extensively in recent years as an activator in crystalline hosts for fast scintillators. The scintillation efficiencies have been found to vary greatly, however. For example, no scintillation is observed from Ce-doped Y2O3 and Lu2O3, the efficiency is low for CeF3, whereas the efficiency is very high for Lu2SiO5:Ce. This behavior has been attributed in large part to the location of the ground 4f and excited 5d levels of Ce3+ with respect to the fundamental band gap of the host. We have performed band structure calculations to predict the band gaps and the location of the Ce and Lu 4f and 5d levels in the fluoride host CeF3 and in the oxide host LuAlO3. Calculations were made using a full-potential linear muffintin orbital (FP-LMTO) approach. We find that Ce 4f levels in CeF3 are several eV above the top of the valence band (VB), thus reducing the probability of hole capture. The Lu 4f levels in LuAlO3 are predicted to be several eV below the top of the VB. Both of these results are in agreement with experiment. Preliminary calculations on LuAlO3:Ce locate the Ce 4f energy levels approximately 3 eV above the VB (O2p) which is not consistent with the high scintillation efficiency of LuAlO3:Ce.

Afterglow and thermoluminescence properties of Lu2SiO5:Ce scintillation crystals

The afterglow and thermoluminescence (TL) properties of several Ce3+ doped Lu2SiO5 crystals are reported. Both properties are caused by the presence of charge traps in the crystals. At least six different glow peaks are observed in the TL glow curve. Each is related to a specific charge trap. The parameters for these charge traps, such as the trap depth and the frequency factor, were obtained from first-order kinetics peak analysis of the TL glow curve. A charge trap with a depth of 1.0 eV is responsible for the afterglow observed at room temperature. Ce3+ ions appear to be the luminescence centres in the recombination process of the trapped charge carriers. It will be shown that optical excitation in the 5d levels of Ce3+ produces trap filling. The possible nature of the charge traps will be discussed.