4f-5d Transition Energy Research Articles

Prediction of 4f-5d Transition Energy of Ce3+ in Oxides By First-Principles Calculations and Machine Learning

A Ce3+ ion has only one electron in the 4f orbitals and its 4f-5d transition energy is strongly influenced by the width of the crystal field splitting of the 5d orbitals. In other words, the absorption and emission wavelengths of Ce3+ in crystals can be widely controlled by changing the ligand field environment. As an example of Ce3+-doped phosphor, Ce:YAG (Y3Al5O12) is widely used as an yellow phosphor for standard white LEDs. Therefore, novel phosphors with desired emission colors can be developed by adding Ce3+ to appropriate host crystals.In this work, we aimed to construct an efficient prediction model for the transition energy of Ce3+ in oxide crystals. Small clusters consisting of the substituted Ce3+ ion and the first-neighbor anions were constructed and molecular orbital calculations were performed using the relativistic discrete-variational Xα (DV-Xα) method. Then machine learning based on structural and electronic state parameters was performed to create a predictive model for the 4f-5d transition energy of Ce3+ in crystals. By creating the correlation diagrams, the influence of each parameter on the transition energy was analyzed in detail.

Optimization of First-Principles Calculation Conditions for Ce3+ in Perovskite-Type Oxides

The 4f-5d transition of Ce3+ in crystals is used in a variety of optical materials, including scintillators and phosphors. It also has the advantages that the wavelength can be controlled by the coordination environment and that Ce3+ is relatively inexpensive among rare earth elements. For the theoretical design of novel Ce3+-doped phosphors, prediction of 4f-5d transition energy by first-principles molecular orbital calculations using model clusters is effective. In general, increase of the cluster size improves the accuracy of calculations and reduces the difference between the experimental and calculated values while very large clusters have the disadvantage of requiring a huge amount of calculation time. Hence, understanding the cluster size dependence is important to determine the efficient and effective cluster size for the first-principles calculations.In this study we focused on Ce3+-doped in YAlO3, and performed first-principles calculations of the 4f-5d transition energies for model clusters with different sizes. At first, the local structures around the Y3+ site of YAlO3 were cut out from the crystal structure. Then the central Y3+ ions of these clusters were replaced by Ce3+ ions. Then the transition energy of Ce3+ in YAlO3 was calculated by the relativistic discrete-variational Xα (DV-Xα) molecular orbital calculations using the Slater's transition state method. The detailed comparison of the results showed that for clusters larger than a certain size, the error between the experimental and calculated values became negligibly small. For comparison, the lattice relaxation was also taken into account by modifying the model clusters using two different methods: the method based on the Shannon's crystal radii and the structural optimization using the CASTEP code, and the results were compared in detail.

First-Principles Analysis of the Effects of Covalency and Ionicity on the 4f-5d Transition Energy of Ce3+ in Garnet-Type Oxides

Abstract A blue light-emitting diode (LED) and a yellow phosphor are frequently combined to create white LEDs, with (Ce3+)-doped YAG as a common phosphor utilized in this process. Yellow light is produced when Ce3+ ions, excited by blue LEDs, are combined with direct blue light to form white light. This study investigated the effects of electronic characteristics, such as covalency and ionicity, on the 5d and 4f level energies of Ce3+ in garnet-type crystals using relativistic discrete variational-Xα (DV-Xα) molecular orbital (MO) calculations. The purpose of this study is to elucidate a detailed mechanism for the centroid shift of the 5d level energies of Ce3+ in crystals based on the MO theory. The theoretical 4f-5d transition energies agreed well with experimental ones, and electronic structure analysis revealed a high correlation between the centroid shift and the net charge of Ce3+. The primary cause of the centroid shift of the 5d level energies relative to the lowest 4f level of Ce3+ in crystals is an increase of the 4f level energies caused by a reduction of the net charge of Ce3+. These results provide a theoretical foundation for the creation of novel Ce3+-doped garnet phosphors for use in displays and solid-state lighting.

Experimental and Theoretical Studies of the Site Occupancy and Luminescence of Ce3+ in LiSr4(BO3)3 for Potential X-ray Detecting Applications.

Ce3+-doped LiSr4(BO3)3 phosphors have been prepared by a high-temperature solid-state reaction method, and structural refinement of the host compound has been performed. The excitation and emission spectra in the vacuum ultraviolet-ultraviolet-visible range at cryogenic temperatures reveal that Ce3+ ions preferentially occupy eight-coordinated Sr2+ sites in LiSr4(BO3)3. Such experimental attribution is well corroborated by the calculated 4f-5d transition energies and defect formation energies of Ce3+ ions at two distinct Sr2+ sites in the first-principles framework. In addition, the doping concentration-dependent luminescence and the temperature-dependent luminescence are systematically investigated by luminescence intensity and lifetime measurements, respectively. This shows that concentration quenching does not occur in the investigated doping range, but inhomogeneous broadening exists in the concentrated samples. With the estimated thermal quenching activation energy, the discussions on the thermal quenching mechanisms suggest that the thermal-ionization process of the 5d electron is a dominant channel for thermal quenching of Ce3+ luminescence, despite the fact that thermally activated concentration quenching cannot be excluded for the highly doped samples. Finally, the X-ray excited luminescence measurement demonstrates the promising applications of the phosphors in X-ray detection.

Mechanistic Insight into Energy‐Transfer Dynamics and Color Tunability of Na4CaSi3O9:Tb3+,Eu3+ for Warm White LEDs

In this work, a latent energy-transfer process in traditional Eu3+ ,Tb3+ -doped phosphors is proposed and a new class of Eu3+ ,Tb3+ -doped Na4 CaSi3 O9 (NCSO) phosphors is presented which is enabled by luminescence decay dynamics that optimize the electron-transfer energy process. Relative to other Eu3+ ,Tb3+ -doped phosphors, the as-synthesized Eu3+ ,Tb3+ -doped NCSO phosphors show improved large-scale tunable emission color from green to red upon UV excitation, controlled by the Tb3+ /Eu3+ doping ratio. Detailed spectroscopic measurements in the vacuum ultraviolet (VUV)/UV/Vis region were used to determine the Eu3+ -O2- charge-transfer energy, 4f-5d transition energies, and the energies of 4f excited multiplets of Eu3+ and Tb3+ with different 4fN electronic configurations. The Tb3+ →Eu3+ energy-transfer pathway in the co-doped sample was systematically investigated, by employing luminescence decay dynamics analysis to elucidate the relevant energy-transfer mechanism in combination with the appropriate model simulation. To demonstrate their application potential, a prototype white-light-emitting diode (WLED) device was successfully fabricated by using the yellow luminescence NCSO:0.03Tb3+ , 0.05Eu3+ phosphor with high thermal stability and a BaMgAl10 O17 :Eu2+ phosphor in combination with a near-UV chip. These findings open up a new avenue to realize and develop multifunctional high-performance phosphors by manipulating the energy-transfer process for practical applications.

Analysis of Energy-Structure Relationship for Ce3+ in Garnet-Type Oxides Based on First-Principles Calculations

The 4f-5d transitions of Ce3+ in crystals are utilized for various optical materials such as solid-state lasers, scintillators, and phosphors. Since the 4f-5d transition energy of Ce3+ in crystals strongly depends on the local structure around Ce3+, it is important to understand the relationship between the energy levels and the local structure for theoretical design of novel optical materials based on Ce3+. In order to control the local structure, garnet-type oxides are useful as host crystals since there are three types of cation sites and the local structure around the impurity Ce3+ ion can be modified widely by cation substitution. In garnet-type oxides, Ce3+ usually occupies the dodecahedral site with D2 symmetry. The arrangement of eight nearest neighbor O2- ions can be understood as interpenetrating two tetrahedrons. Therefore, the geometry of CeO8 cluster can be specified by six structural parameters corresponding to the coordinates of two representative ligand positions. However, investigation of the energy-structure relationship depending on six structural parameters is not straightforward. In this work, in order to visualize the energy-structure relationship of Ce3+ occupying the dodecahedral site in garnet-type oxides, two-dimensional energy maps were constructed by performing first-principles relativistic molecular orbital calculations for a series of CeO8 clusters constructed by changing two selected structural parameters. The 4f-5d transition energies of Ce3+ for these clusters were calculated based on the Slater’s transition state method. Then the relationship between the 4f-5d transition energy and the local structure depending on the six structural parameters was clarified by the combination of these energy maps.

First-Principles Calculations of 4f-5d Transition Energy of Ce3+ in Y(Al1-xGax)5O12

The crystals doped with Ce3+ are utilized as various optical materials such as solid-state lasers, scintillators, and phosphors. Since the 4f-5d transition energy of Ce3+ in crystals strongly depends on the coordination environment, it is important to understand the relationship between the energy levels and the coordination environment for theoretical design of novel optical materials. For this purpose, garnet solid solutions are useful as host crystals since the physical properties can be modified by forming variety of solid-solutions through cation substitution. For example it is known that the 4f-5d transition energy of Ce3+ in Y(Al1-xGax)5O12 increases monotonically as x increases [1]. In this work, in order to investigate the relationship between the 4f-5d transition energy and the coordination environment of Ce3+ in Y(Al1-xGax)5O12, first-principles calculations were performed using the relativistic DV-Xα molecular orbital method [2]. At first YO8 clusters with D2 symmetry were constructed based on the crystal structure of Y(Al1-xGax)5O12 [3,4]. Then Ce was substituted for Y and the Ce-O bond lengths were adjusted based on the Shannon’s crystal radii [5] so as to consider the lattice relaxation effect [6]. In order to produce the effective Madelung potential, point charges were located at the atomic sites outside the cluster. As the exchange-correlation potential, the VWN potential [7] with the relativistic correction [8] was adopted. The 4f-5d transition energy was calculated using the Slater’s transition state method [9]. The calculated results showed that the variations of the average energy and the crystal field splitting of 5d levels of Ce3+ depending on x can be understood by the variations of the bond lengths, they are not monotonic. Although the 4f-5d transition energy is basically determined by these factors, interestingly the resultant theoretical 4f-5d transition energy showed monotonic variation. As a result the experimentally observed increasing tendency of the 4f-5d transition energy for increasing x was well reproduced. [1] P. Dorenbos, J. Lumin., 134, 310 (2013). [2] A. Rosén, D.E. Ellis, H. Adachi, and F.W. Averill, J. Chem. Phys., 65, 3629 (1976). [3] A. Nakatsuka, A. Yoshiasa, and S. Takeno, Acta Crystallogr., B51, 737 (1995). [4] A. Nakatsuka, A. Yoshiasa, and T. Yamanaka, Acta Crystallogr., B55, 266 (1999). [5] R.D. Shannon, Acta Crystallogr., A32, 751 (1976). [6] S. Watanabe, T. Ishii, K. Fujimura, and K. Ogasawara, J. Solid State Chem., 179, 2438 (2006). [7] S. H. Vosko, L. Wilk, and M. Nusair, Can. J. Phys. 58, 1200 (1980). [8] A. H. MacDonald and S. H. Vosko, J. Phys. C12, 2977 (1979). [9] J. C. Slater, Quantum Theory of Molecules and Solids (McGraw-Hill, New York, 1974), Vol. 4.

(Luminescence and Display Materials Division Centennial Outstanding Achievement Award) Vacuum Referred Electron Binding Energies in Impurity and Host Band States as Revealed from Empirical Studies; a Personal Account

It is about 20 years ago that I started to collect data from literature on the 4f-5d transitions energies of the lanthanides in inorganic compounds. This curiosity driven research was inspired by my desire to understand why and how the emission from Ce3+, applied as luminescence activator in scintillation crystals, changes with type of compound. It was also inspired by observations and reports on constant energy differences between 4f-5d transition energies when that of Ce, Pr, and Nd in the same compound are compared. Today, data has been collected on 2000+ compounds with information on all divalent and all trivalent lanthanides extracted from 7000+ manuscripts. Information that comprises not only 4f-5d transitions but also VBàLn charge transfer band energies, host exciton energies, luminescence decay and quenching data. The data base is current being augmented with data on the 6s2-elements and transition metal elements. Figure 1. A typical VRBE diagram, here for LaAlO3, illustrating the location of Ln2+ 4f-levels (in red) and Ln3+ 4f-levels (in blue). Open data symbols are the VRBE in the lowest energy Ln3+ level. A brief overview on the methods and models derived from this curiosity driven research is presented. Particularly, attention is focussed on the chemical shift model that enables to construct so-called vacuum referred binding energy (VRBE) diagrams as illustrated in Figure 1. It is a unique method that provides information on the VRBE at the top of the valence band and the bottom of the CB in a routine fashion. The electronic structure of inorganic compounds can be compared with each other with reference to a common energy, i.e., the energy of an electron at rest in vacuum. Figure 2 shows a stacked VRBE diagram. It turns out that when comparing different compounds with each other, the VRBE in the lanthanide 4fn ground state levels show much less variation than the VRBE at the conduction band bottom or valence band top. This illustrates that in order to understand (electronic) structure property relationships we should understand what controls the VRBE at the CB-bottom and VB-top rather than what controls the VRBE in the 4fn ground state. Figure 2. A stacked diagram of VRBE schemes of various oxide compounds illustrating that the lanthanide 4f ground state levels of Eu2+ and Ce3+ are fairly compounds invariant but that host band energies change widely. Problem with such new insight is that rarely VRBE information is provided. Photo-electron spectroscopy techniques and ab-initio or first principles calculations commonly relate energies with respect to the Fermi energy but not to the vacuum level. Electrochemistry does make use of a common energy reference. This is the standard hydrogen potential, and since that potential is equivalent to -4.44 eV on the VRBE-scale, one may, although rarely done so, translate redox potentials into VRBE energies. This means that data on redox potentials, as is abundantly available in the studies on materials for photo-catalytic splitting of water, can be used to derive VRBE energies. In Li-ion battery research, the common reference is the Li0/+ redox potential, and again the data on materials for battery research can be translated into VRBE data. Above demonstrates that the different disciplines; luminescence materials, materials for catalysis, and materials for batteries are “speaking their own languages”. However, as a matter of fact, many properties relate to one and the same, i.e., the binding energy of electrons with respect to the vacuum level. I will demonstrate how the different disciplines connect and how insight from luminescence studies may be of use to the other disciplines and vice versa. Figure 1

Investigation on Structure-Energy Relationship for Ce3+ Coordinated with Six or Eight Oxygen Ions Based on First-Principles Calculations

As a red phosphor to improve the color rendering index of white LEDs, (Sr,Ca)AlSiN3:Eu phosphor is widely used. However, since the production cost of this phosphor is high, cheaper alternative is strongly desired. As an alternative, Mn4+-doped fluoride phosphor has been recently put into practical use [1]. In the case of oxide host, however, the shortest emission wavelength reported for Mn4+ is ca. 650 nm [2] which is still longer than 630 nm required for the red phosphor for white LEDs. Therefore, establishment of a design guideline to decrease the emission wavelength for Mn4+-doped oxide phosphor is an important issue. In order to provide such information, we have recently constructed the energy level diagrams and maps for Mn4+ in oxides based on first-principles calculations [3]. On the other hand, Ce3+ phosphor is also a candidate for the red phosphor for white LEDs. In this case, the emission wavelength is much shorter than 630 nm in the case of oxide host. Therefore, a design guideline to increase the emission wavelength is required. Recently an emission at ca. 600 nm was reported for Ce3+ at a six-coordination site in Sr6Y2Al4O15 [4]. In this crystal, there are several sites which can be occupied by Ce3+. However, only Ce3+ at the six-coordination site shows red emission, while Ce3+ at eight- or nine- coordination sites show blue emission. In this work, in order to clarify the effect of local structures such as coordination number, bond length, and symmetry on the energy levels of Ce3+, first-principles relativistic molecular orbital calculations were performed for model clusters with various local structures, and the energy level diagrams and maps were constructed. As model clusters, CeO6 9- and CeO8 13- clusters with Oh or D4h symmetries were constructed. The first-principles relativistic molecular orbital calculations were performed using the relativistic SCAT code [5]. The calculations were performed for clusters with gradually changed bond lengths and bond angles. Various energy level diagrams and maps depending on the bond length and the bond angle were constructed by connecting the obtained orbital energies. The energy level diagram for CeO6 9- cluster with Oh symmetry shows that both the crystal field splitting of 5d level and that of 4f level increase as the bond length decreases. As a result, the 4f level and 5d level begin to overlap at ca. 1.9 Å. The relationship between the 4f-5d transition energy and the local structure was also clarified based on various energy diagrams and maps. Such information would be useful for the theoretical search of the novel Ce3+-doped oxide red phosphor for white LEDs.

Creation of 4fn-4fn-15d1 Transition Energy Diagram of Trivalent Lanthanide Ions in Fluorides Based on First-Principles Calculations

The theoretical prediction of the 4fn-4fn-15d1 transition energies of lanthanides in crystals is an important issue in the development of novel luminescent materials such as solid-state lasers or phosphors. In our previous work, the first-principles calculations of the entire multiplet structures of lanthanide (Ln) ions in LiYF4 (YLF) corresponding to 4fn and 4fn-15d1 configurations were performed using the relativistic discrete variational multi-electron (DVME) method [1]. However, the lowest 4fn-4fn-15d1transition energy was overestimated for light lanthanides while it was underestimated for heavy lanthanides. In this work, in order to improve the accuracy of the theoretical transition energy, a correction based on the molecular orbital (MO) calculation in the Slater’s transition state was introduced. The LnF8 clusters were constructed based on the crystal structures of YLF and CaF2. The fully-relativistic MO calculations were performed using the relativistic DV-Xα code. The multiplet calculations were performed using the relativistic DVME code. The Slater determinants corresponding to 4fn and 4fn-15d1 configurations were constructed from the four-component relativistic MOs and used as the basis functions to diagonalize the relativistic many-electron Hamiltonian. In order to correct the errors in the transition energy, MO calculations in the Slater’s transition state where a half electron was excited from the Ln 4f level to the Ln 5d level were also performed. A constant correction term was added to the diagonal matrix element of the many-electron Hamiltonian for 4fn-15d1 configuration so that the 4fn -4fn-15d1transition energy is consistent with the 4f-5d transition energy obtained by the MO calculation in the Slater’s transition state. The diagrams representing the lowest 4fn-4fn-15d1transition energies of trivalent lanthanide ions in YLF calculated with and without the above correction are shown in Fig. 1. The overestimation in the light lanthanides and the underestimation in the heavy lanthanides are significantly reduced by the correction and the theoretical transition energies approached to the experimental values in the literature [2-5].

Role of oxygen vacancy on the photoluminescence of BaMgSiO4:Eu phosphors: experimental and theoretical analysis.

Pure BaMgSiO4:Eu(2+) phosphor, prepared by a solid state reaction method under N2 atmosphere, exhibited a strong green emission at 500 nm and a weak emission at 405 nm. Heat treatment under NH3 atmosphere causes changes in the PL intensity: the green emission at 500 nm gradually decreases and completely disappears after heat treatment for 3 h, whereas a new blue emission peak, centered at 445 nm, appears and becomes very strong. The results of the analyses with electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) spectroscopy suggest that the heat treatment causes the generation of a large amount of oxygen vacancies. This resulted in the aforementioned color changes of the BaMgSiO4:Eu phosphor, which are confirmed by the results of DFT+U calculations. In particular, these calculations showed that Eu prefers to occupy Ba(3) sites, which are six coordinated to oxygen atoms. The emission at 500 nm was attributed to the 4f-5d transition energy of Eu in Ba(3) site, calculated as 2.54 eV. It was also shown that Eu 4f energy level decreases when oxygen is removed from the oxygen position adjacent to Eu, which results in a larger Eu 4f-5d transition energy and shorter wavelengths of emission peaks.

Ab initio theoretical study of the [formula omitted] and 4f75d manifolds of Tb3+-doped BaF2 cubic sites

An ab initio model potential embedded cluster study on the 4f8 and 4f7 5d manifolds of the long range compensated, cubic, substitutional Tb3+ defects of Tb-doped BaF2 is presented here. 4f–4f and 4f–5d transition energies and 4f–5d absorption electric dipole oscillator strengths for the dipole allowed transitions are reported and comparisons with emission and excitation experimental spectra are presented. We find good agreement with the energies of the experimental 4f–4f green and blue emissions. The characteristic features of the 4f–5d excitation spectrum (spin allowed vs. spin forbidden transitions) are well reproduced by the calculations. The transition energies from the ground state to the different spin nonet and spin septet levels of the 4f7 5d configuration of this ion in the center of the lanthanide series show an error of around 10%, which is in line with previous calculations on other lanthanide ions with lower spin multiplicities and simpler manifolds at the beginning and at the end of the series. The calculation supports a recent assignment of experimental excitation bands between 54,000 and 66,000cm−1 as 4f→5d(t2g) transitions. On the other hand, a new assignment is made of the highest band in the excitation spectrum at around 76,000cm−1: it corresponds to transitions to levels of the 4f7 5d configuration with the 4f7 subshell in the excited 6P term, rather than to a Tb-bound exciton. Preliminary studies on excitonic states of Tb-doped BaF2 indicate that energy levels that can be characterized as Tb-trapped excitons are found in the same spectral region as the spin forbidden 4f→5d(t2g) transitions at ground state Tb–F distances, and their energy lowers very much at shorter Tb–F distances.

A Review on How Lanthanide Impurity Levels Change with Chemistry and Structure of Inorganic Compounds

The energy of the 4f-5d transitions of divalent and trivalent lanthanide impurities in compounds depends strongly on the type of lanthanide, its valence, and the type of compound. Despite this large variability there is much systematic in 4f-5d transition energy. Once it is known for one lanthanide that for all others when in the same compound can be predicted. The same applies for the energy of electron transfer from the valence band to the 4f-shell of lanthanides which also behaves in a systematic fashion with type of lanthanide and type of compound. This work reviews my studies during the past fifteen years that are based on an analysis of data on all divalent and all trivalent lanthanides in more than 1000 different inorganic compounds collected from the archival literature. The established redshift and charge transfer models that form the basis to construct binding energy schemes showing all lanthanide levels with respect to the host bands are reviewed and the latest developments are addressed.

Ab Initio Calculation of Electronic Structure and 4f–5d Transition Energies of Ce3+ Doped in Y3Al5O12 Nanocrystals

The elementary-state electronic structure and 4f-5d transitions of Y3Al5O12:Ce3+ nanocrystals simulated by several clusters were computed by the ab initio self-consistent relativistic DV-X alpha (discrete variational X alpha) method. A 35-ion cluster was chosen to simulate the local surroundings of Ce3+ doped in Y3Al5O12 bulk crystals while four additional smaller irregular clusters were also chosen to simulate the local surroundings of Ce3+ ions in nanocrystals. Besides obtaining the elementary-state 4f and 5d electronic structure, based on the transition-state calculations we also obtained the five 4f-5d transition energies for each of these clusters. We found that compared with the bulk crystals, for all the clusters simulating nanocrystals the first 4f-5d transition peak (the lowest energy peak) was blueshifted, and the second peak was redshifted a little, which are both in accordance with the observed experimental excitation spectra of 5d luminescence of Y3Al5O12:Ce3+. We fitted the observed first two transition peaks in a published experimental excitation spectrum of nanocrystals by weighted summing of the excitation spectra of the selected clusters; therefore, the weight contribution of each cluster was obtained. Moreover, the other three unobserved peaks were all expected to be redshifted. According to these calculations and our understanding, in Y3Al5O12:Ce3+ nanocrystals, the shift of the peaks can be mainly attributed to the reduction of the crystal field felt by Ce3+ ions-which results in the reduction of the splittings of 5d levels of Ce3--as well as to the increase of the difference between the 5d average level and the 4f average level of Ce3+.

Mechanism of Luminescence Enhancement in Ca4YO ( BO3 ) 3 : Eu3 + by Gd Substitution under Vacuum Ultraviolet Light Excitation

The role of in enhancing luminescence intensity of under excitation by vacuum UV light was investigated. A dominant excitation band peaked at is assigned to the transitions from O 2p valence state to mixed states of B 2p and Y 4d orbitals on the basis of calculation by the relativistic method, which is a popular computational code of the molecular orbital calculation. The band is related also to , because its intensity increases with Gd molar fraction. Presumably excitation energy absorbed by the above transitions is transferred to via the 4f excited levels of , because both the charge transfer and 4f–5d transition energy of are much higher than the photon energy of the band.

Ab initiocalculation of the contribution from anion dipole polarization and dynamic correlation to4f−5dexcitations ofCe3+in ionic compounds

In this study basic effects are investigated of ion-host interactions on 4f-5d excitations of Ce 3+ ions in wideband ionic host compounds. Particularly the shift of the average 4f-5d transition energy compared to that of the free ion, the centroid shift, is of interest. The self-induced dipole effect where the 4f or 5d electron dynamically polarizes the neighboring ions is analyzed in detail. Taking into account the overlap of the 5d orbital of Ce 3+ with the neighbor anions, the standard classical expression was modified, and the result is that this not only drastically reduces the value of the polarization contribution to the centroid shift but also the steep dependence on the distance to the anions almost vanishes. This polarization effect and the additional contributions such as covalency and dynamic correlation should be included in a configuration interaction CI calculation applied on a cluster of ions around the Ce 3+ ion. Calculations with Hartree-Fock Moller-Plesset perturbation theory corrected to second order for perturbation effects and coupled-cluster theory with single, double, and triple excitations were conducted with various basis sets and cluster sizes and it turned out that the results do not include the polarization effect and so this contribution had to be calculated separately and was added to the CI results. Good agreement at the 0.15 eV level is obtained between theory and experiment for Ce 3+ in BaF2, LaAlO3, and LaCl3.

Spectroscopy and Lanthanide Impurity Level Locations in CaGa2 S 4 : Ln3 + ( Ln = Ce , Pr , Tb , Er , Tm )

The emission and excitation spectra of single crystals of doped with and were measured with the aim to determine the location of the lanthanide energy levels relative to the valence and conduction band of the host crystal. By combining energies known for charge transfer bands involving trivalent lanthanides with systematic behavior in 4f-5d transition energies of divalent lanthanides, the level positions of 4f and 5d states for each divalent lanthanide can be drawn relative to the host levels. With similar techniques combined with results on the thermal quenching behavior of emission, the levels for the trivalent lanthanides were constructed. We demonstrate consistency between the proposed level scheme and the spectroscopic information presented here and elsewhere. The scintillation properties of -doped are addressed also. © 2004 The Electrochemical Society. All rights reserved.

Predictability of 5d level positions of the triply ionized lanthanides in halogenides and chalcogenides

Information on 4f–5d transition energies of the triply ionized lanthanides ( Ce 3+, Pr 3+,…, Lu 3+) in over 300 different compounds has been gathered, analyzed and occasionally re-interpreted. Some of the main results will be presented. New estimates will be given for the energy of the first electric dipole allowed and some of the spin forbidden fd transitions of the free (gaseous) triply ionized lanthanides.

Determination of the Ce+3 bonding in the Ca0.5Sr0.5Ga2S4:Ce phosphor via x-ray photoelectron spectroscopy

The addition of oxygen in Ca0.5Sr0.5Ga2S4:Ce phosphor was found to nearly double the luminance and to blue shift the emission spectrum of the Ce+3 4f–5d transition. X-ray photoelectron spectroscopy (XPS) analysis was used to investigate the local chemistry of the Ce+3 luminescent center in the undoped and oxygen-doped Ca0.5Sr0.5Ga2S4 phosphor. The shake up structure in the Ce+3 3d3/2 and 3d5/2 XPS spectra is due to a ligand-to-metal charge transfer process, and the relative intensity of the charge transfer peaks increased when oxygen was introduced. Because the charge transfer probability is controlled by the local ionicity of the Ce bonds, the increase in the charge transfer peak intensity is consistent with the formation of Ce–O bonds. Furthermore, the binding energy of the charge transfer peaks and the Ce MNN Auger peak shifted, again consistent with oxygen bonding to the Ce+3 luminescent center. A self-consistent field configuration interaction model is used to calculate the positions of the 4f and 5d levels with Ce–S and Ce–O bonds. By replacing the three of eight sulfur ligands with oxygen the SCF/CI model predicted a 1035 cm−1 blue shift in the 4f–5d transition energy which was in excellent agreement with the observed 730 cm−1 blue shift.