Pieter Dorenbos

The 5d level positions of the trivalent lanthanides in inorganic compounds

Abstract The literature on 4f n ↔4f n −1 5d transitions of the trivalent lanthanides in inorganic compounds has been collected. From critically analyzing fd-excitation, absorption, reflection and df-emission spectra, values for the spectroscopic red shift of 5d levels and the stokes shift were determined. Data pertaining to 368 different lanthanide sites in over 300 different compounds (fluorides, chlorides, bromide, iodides, oxides, sulfides, selenides and oxy-nitrides) has been compiled. From the data, it is possible to predict for each of the 12 lanthanide ions ( Ce 3+ , Pr 3+ until Yb 3+ ) doped in any of the compounds compiled, the position of the lowest 5d levels with typically ±600 cm −1 accuracy.

Energy of the first 4f7→4f65d transition of Eu2+ in inorganic compounds

Abstract fd-excitation, absorption, reflection, and df-emission spectra presented in the literature on Eu2+ in inorganic compounds have been gathered and re-analyzed. Emission wavelength, width of the emission band, absorption wavelength, Stokes shift, and redshift pertaining to Eu2+ in more than 300 different compounds (fluorides, chlorides, bromide, iodides, oxides, sulfides, selenides, and nitrides) are presented. From the data, it is possible to predict for each of the 13 lanthanide ions (La2+, Ce2+, Pr2+, until Yb2+), doped in any of the compounds compiled, the energy of the transition from the 4fn ground state to the first 4fn−15d level and also the energy of df-emission. A brief overview on the relationships between redshift, Stokes shift, and the width of the emission with the type of compound is given.

The 4fn↔4fn-15d transitions of the trivalent lanthanides in halogenides and chalcogenides

Abstract Information from the literature on the energy difference between the 4 f n ground-state multiplet and the low lying 4 f n−1 5 d excited states of Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Er3+, Tm3+ and Yb3+ doped in about 60 different inorganic compounds has been gathered and studied. It will be demonstrated that once the energy of the first spin allowed 4 f n →4 f n−1 5 d transition in any of the above-mentioned lanthanides in a specific compound is known, the corresponding transition energy of all other lanthanides if doped in that same compound can be predicted with an accuracy of typically ±600 cm −1 . New estimates will be given for the energy of the first spin-allowed and some of the spin-forbidden fd transitions of all the free (gaseous) triply ionized lanthanides.

High-energy-resolution scintillator: Ce3+ activated LaBr3

The scintillation properties of LaCl3 doped with 10% Ce3+ are presented. Under optical and gamma ray excitation, Ce3+ emission is observed to peak at 330 and 352 nm. The scintillation light output is 46 000±1000 photons/MeV at 662 keV. Forty percent is emitted with a decay time of 26 ns, 30% with 210 ns, and 30% with about 1000 ns. An energy resolution (full width at half maximum over the peak position) of 3.3±0.3% was observed for the 662 keV full absorption peak.

Mechanism of Persistent Luminescence in Eu2+ and Dy3+ Codoped Aluminate and Silicate Compounds

A mechanism of persistent luminescence that was proposed in 1996 for SrAl2O4:Eu2+;Dy3+ has been widely adopted to explain afterglow in many Eu2+ and Dy3+ codoped aluminates and silicates. The mechanism involves the thermally activated release of a hole from Eu2+ in its excited 5d state to the valence band which is subsequently trapped by Dy3+. In this work the location of the lanthanide energy levels relative to the valence and conduction band of various compounds is presented. It is shown that the mechanism of persistent luminescence cannot be correct. An alternative model that involves the ionization of the 5d electron to conduction band states and subsequent trapping by Dy3+ is proposed. The level schemes are consistent, both qualitatively and quantitatively, with many observations regarding persistent luminescence. They also provide insight into the mechanism of thermal quenching of Eu2+ 5d-4f emission.

Relation between Eu2+ and Ce3+ f ↔ d-transition energies in inorganic compounds

Data available on the fd-transition energies of Ce3+ in inorganic compounds are compared with those of Eu2+ in the same compounds. Despite differing charge compensating defects, clear correlation was found. The redshift of absorption, the Stokes shift of emission, the centroid shift of the 5d configuration and the total crystal field splitting of the 5d levels of Eu2+ and Ce3+ all appear to be linearly related to one another. The values for Eu2+ are about 0.7 times those for Ce3+. This implies that spectroscopic properties known for Ce3+ can be employed to roughly predict spectroscopic properties for Eu2+ and vice versa. The findings for Ce3+ and Eu2+ can be generalized to all trivalent and divalent lanthanides.

5d-level energies of Ce3+ and the crystalline environment. IV. Aluminates and simple oxides

Information on the energy of 5d-levels of Ce3+ ions in aluminates and “simple” oxides has been collected. The crystal field splitting of the 5d-levels is interpreted in terms of the type and size of anion polyhedron coordinating the Ce3+ ion. The centroid (barycenter) shift of the 5d-configuration is analyzed by a ligand polarization model providing values for the spectroscopic polarizability αsp of the anion ligands. The data provide evidence that the centroid shift behaves independently from the crystal field splitting. By combining centroid shift and crystal field splitting, the “spectroscopic” redshift of the first electric dipole-allowed fd transition of Ce3+-doped in the compounds will be interpreted. The large crystal field splitting in garnet compounds and the small splitting in perovskite compounds will be discussed.

f → d transition energies of divalent lanthanides in inorganic compounds

The systematic in the 4f n ? 4f n?1 5d transition energy of divalent lanthanides in inorganic compounds has been studied. Energies were derived from excitation and optical absorption spectra gathered from the literature. Going through the lanthanide series from La2+ to Yb2+, a characteristic variation is observed similar to that known for the trivalent lanthanides and the free atoms and free ions. Once the transition energy is known for one lanthanide in a compound, that of all others in that same compound can be predicted. The value for the Stokes shift between fd excitation and df emission appears independent of the lanthanide ion. For Gd2+ to Yb2+ both the spin-forbidden and the spin-allowed fd-transition energies are discussed.

Light output and energy resolution of Ce3+ -doped scintillators

The systematic trends regarding wavelength of emission, maximum obtainable scintillation light output, gamma-ray energy resolution, and scintllation decay time of Ce3+-doped fluorides, chlorides, bromides, iodides, oxides, sulfides, and selenides are reviewed. Theoretical limits will be compared with actually achieved values. The relation between energy resolution and non-proportional response of scintillators will be discussed.

Advances in Yield Calibration of Scintillators

By means of a photomultiplier tube, a Si-photodiode, and a Si-avalanche photodiode, the absolute scintillation yield of recently developed LaBr₃:Ce, LaCl₃:Ce, and (Lu,Y)₂SiO₅:Ce scintillators and traditional Lu₂SiO₅:Ce, Bi₄Ge₃O₁₂, NaI:Tl, CsI:Tl, and CsI:Na scintillators were determined. These are all well known scintillators that cover emission wavelengths from 250 nm to 750 nm. By comparing the scintillation yield independently measured with the three different photon detectors reliable yield values are obtained.