Experimental Stark Levels Research Articles

Investigation of J – J “mixing” mechanism influence on optical and magnetooptical properties of praseodymium yttrium-aluminum garnet PrYAG

The spectra of the luminescence and magnetic circular polarization of luminescence (MCPL) in the praseodymium yttrium garnet aluminate Pr3+:YAG (PrYAG) have been studied within the visible spectral range at temperature T = 300 K. Analysis of the spectral dependences of the magnetooptical and optical spectra has made it possible to identify the optical 4f → 4f transitions occurring between the Stark sublevels of the 3P0, 3P1 and 3H5, 3H6 multiplets in PrYAG. It has been shown that for this paramagnetic garnet in the MCPL degree spectrum for the “green” luminescence band associated with forbidden 4f→ 4f transitions 3P0 → 3H5 within the visible spectral range, a significant role is being played by the effect of quantum mechanical J - J “mixing” of the energy states of Stark singlets of the 3H5 and 3H6 multiplets of the non-Kramers rare-earth (RE) Pr3+ ion. A parameterized Hamiltonian defined to operate within the entire 4 f(2) ground electronic configuration of Pr3+ was used to model the experimental Stark levels, their irreducible representations (irreps.) and wavefunctions. Nine independent CF parameters, Bqk, were optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 61 calculated-to-experimental levels is 17.86 cm–1.

Some interesting features of the Tb3+ magnetooptics in the paramagnetic garnets

The spectra of the absorption, luminescence, magnetic circular dichroism (MCD) and magnetic circular polarization of luminescence (MCPL) in the terbium–yttrium gallium garnet Tb3+:Y3Ga5O12 (Tb:YGG) have been studied within the visible and near ultraviolet (UV) spectral range for temperatures T=85 and 300K. The MCD spectrum observed within the UV absorption band for Tb:YGG is associated with spin- and parity-allowed electric-dipole 4f→5d transitions occurring between levels of the ground 7F6 multiplet and the 7D state of the excited 4f(7)5d configuration of the Tb3+ ion. Analysis of the spectral and the temperature dependences of the magnetooptical and optical spectra has made it possible to identify magneto-optically-active 4f→4f transitions occurring between Stark sublevels of the 5D4 and 7F5 multiplets in Tb3+:YGG. Quantum mechanical “mixing” of the three lowest energy Stark singlets in the excited 5D4 multiplet by an external magnetic field H leads to the change of the circularly polarized luminescence line intensities. The Zeeman effect in the UV absorption band 7F6→5L10 of Tb3+:YGG at T=85K was also studied. The magnetic field dependence of the Zeeman splitting of some absorption lines is found to exhibit unusual behavior: as the magnetic field increases, the band splitting decreases rather than increases. A parameterized Hamiltonian defined to operate within the entire 4f(8) ground electronic configuration of Tb3+ was used to model the experimental Stark levels, their irreducible representations (irreps.) and wave functions. The crystal-field parameters were determined using a Monte-Carlo method in which nine independent crystal-field parameters, were given random initial values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 101 calculated and experimental Stark levels is 16.7cm−1.

Magnetooptics of non-Kramers Eu3+ ions in garnets: analysis complemented by crystal-field splitting modeling calculations

Spectra of absorption, luminescence, magnetic circular dichroism (MCD), and magnetic circular polarization of luminescence (MCPL) in Gd3Ga5O12:Eu3+ and Eu3Ga5O12 garnets were studied within the visible spectral range at 300 K. Analysis of the spectral and temperature dependences of the magnetooptical and optical spectra made it possible to identify the magneto-dipole (MD) and electro-dipole (ED) 4f→4f transitions occurring between Stark sublevels of the 7FJ (J=1, 2) and 5D0 multiplets in Eu3+-containing garnet structures. Quantum mechanical “mixing” had significant influence on quasi-degenerate states of the non-Kramers rare-earth Eu3+ ion for Eu3Ga5O12 in MCD due to forbidden MD transition 7F1→5D0 and for Gd3Ga5O12:Eu3+ in MCPL due to MD 4f→4f transition 5D0→7F1 and forced ED-transition 5D0→7F2. A parameterized Hamiltonian defined to operate within the entire 4f(6) ground electronic configuration of Eu3+ ion was used to model the experimental Stark levels, including their irreducible representations and wavefunctions. The crystal-field parameters were determined through a Monte-Carlo method in which nine independent crystal-field parameters, Bkq, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental levels was 0.73 meV.

Analysis of the optical and magnetooptical spectra of non-Kramers Pr3+(4f2) in Y3Al5O12 complemented by crystal-field modelling

The spectra of the absorption, luminescence, magnetic circular dichroism (MCD) and magnetic circular polarization of luminescence (MCPL) in the praseodymium yttrium garnet aluminate Pr3+:YAG have been studied within the visible and near ultraviolet (UV) spectral range for temperature T=90K and 300K. Analysis of the spectral and the temperature dependences of the magnetooptical and optical spectra has made it possible to identify the optical 4f→4f transitions occurring between the Stark sublevels of the 1D2, 3P0 and 3H4 multiplets in Pr3+:YAG. It has been shown that for Pr3+:YAG in the MCD within the UV spectral range for the absorption bands due to allowed 4f→5d transitions, and also in the MCPL for the luminescence bands, respectively, due to forbidden 4f→4f transitions within the visible spectral range, a significant role is being played by the effect of quantum mechanical “mixing” of the states of the three lowest energy Stark singlets of the ground state 3H4 multiplet of the non-Kramers RE Pr3+ ion. A parameterized Hamiltonian defined to operate within the entire 4f2 ground electronic configuration of Pr3+ was used to model the experimental Stark levels, their irreducible representations (irreps) and wave functions. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, Bqk, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 61 calculated to experimental Stark levels is 18cm−1.

Crystal-field analysis and Zeeman splittings of energy levels of Nd3+ (4f3) in GaN

The crystal-field splitting and Zeeman splitting of energy levels of Nd3+ (4f3) doped into semi-conducting GaN (3.2 eV) grown in the hexagonal (huntite) phase by plasma-assisted molecular beam epitaxy have been modeled using a parameterized Hamiltonian defined to operate within the complete 4f3 electronic configuration of Nd3+ substituted for Ga3+ in the lattice. Zeeman splittings were obtained by applying magnetic fields up to 6.6 T with the fields parallel and perpendicular to the crystallographic c-axis. The experimental energy (Stark) levels were obtained from a recent spectroscopic study on the same samples, where the combined excitation emission spectroscopy (CEES) identified the majority of Nd3+ ions as replacing Ga3+ in sites of C3v symmetry. The manifolds of Nd3+ (4f3)2S+1LJ modeled for the crystal-field splitting include the ground state, 4I9/2, and excited states 4I11/2, 4I13/2, 4F3/2, 4F5/2, 2H9/2, 4F7/2, 4S3/2, 4G5/2, and 4G7/2. The energies of 41 experimental Stark levels from these manifolds were modeled through the use of a Monte Carlo method in which independent crystal-field parameters (CFP) were given random starting values and optimized using standard least-squares fitting between calculated and experimental Stark levels. Irreducible representations (irreps) and crystal field quantum numbers (μ) were assigned to the energy level states of the 4I9/2 and 4F3/2 multiplet manifolds based on an analysis of the Zeeman data. This allows determination of which of the competing local minima should be considered to be the physically significant minimum. Using standard least-squares fitting between calculated and experimental Stark levels for Nd3+ in C3v symmetry, we obtain a final standard deviation of 7.01 cm−1 (rms = 5.48 cm−1).

Spectroscopic analysis of Eu3+ in single-crystal hexagonal phase AlN

A detailed spectroscopic analysis of the crystal-field splitting of the energy levels of Eu3+(4f6) in single crystals of hexagonal phase aluminum nitride is reported based on assignments made to the high-resolution cathodoluminescence spectra observed between 500 nm and 750 nm obtained at 11 K and room temperature. Single crystals doped with trivalent europium were grown by high pressure, high temperature technology, and the crystal structure was confirmed by x ray diffraction methods to be the hexagonal phase. The Eu3+ ions substitute for Al3+ ions in sites of C3v symmetry during crystal growth. More than 97% of the observed spectra are attributed to Eu3+ in the majority site. The spectra are identified as transitions from the excited 5D0 and 5D1multiplets of Eu3+ to the ground-state multiplets 7F0, 7F1, 7F2, 7F3,7F4, 7F5, and 7F6 split by the crystal field into energy (Stark) levels. A parameterized Hamiltonian defined to operate within the 4f6 electronic configuration of Eu3+ was used to model the experimental Stark levels and their symmetry assignments or irreducible representations (irreps). The crystal-field parameters were determined through use of a Monte Carlo method in which the six Bqk were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting, which involved 20 Stark levels and their irreps from 5D1, 5D0, and 7F0–4, resulted in a rms deviation of 6.7 cm−1. The predicted splitting of the 7F5 and 7F6 multiplets was used to assign the experimental splitting for these manifolds since the spectra involved are weak and broad, precluding detailed Stark-level assignments.

Spectra, energy levels, and symmetry assignments for Stark components of Eu 3+(4f 6) in gadolinium gallium garnet (Gd 3Ga 5O 12)

Absorption and fluorescence spectra observed between 450 and 750 nm at 85 K and room temperature (300 K) are reported for Eu 3+(4f 6) in single-crystal Czochralski-grown garnet, Gd 3Ga 5O 12 (GGG). The spectra represent transitions between the 2 S+1 L J multiplets of the 4f 6 electronic configuration of Eu 3+ split by the crystal field of the garnet. In absorption, Eu 3+ transitions are observed from the ground state, 7F 0, and the first excited multiplet, 7F 1, to multiplet manifolds 5D 0, 5D 1, and 5D 2. The Stark splitting of the 7F J multiplets ( J=0–6) was determined by analyzing the fluorescence transitions from 5D 0, 5D 1, and 5D 2 to 7F J . The Eu 3+ ions replace Gd 3+ ions in sites of D 2 symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2 J+1 non-degenerate Stark levels characterized by one of four possible irreducible representations (irreps) assigned by an algorithm based on the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels in D 2 symmetry. The quasi-doublet in 5D 1 was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between 5D 1 and 7F 1. A parameterized Hamiltonian defined to operate within the entire 4f 6 electronic configuration of Eu 3+ was used to model the experimental Stark levels and their irreps. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, B q k , were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental Stark levels is 5.9 cm −1. The choice of coordinate system, in which the nine B q k are real and the crystal-field z-axis is parallel to the [0 0 1] crystal axis and perpendicular to the xy plane, is identical to the choice we used previously in analyzing the spectra of Er 3+ and Ho 3+ garnets.

Energy levels and symmetry assignments for Stark components of Ho3+(4f10) in yttrium gallium garnet (Y3Ga5O12)

Absorption and fluorescence spectra observed between 1950 and 320 nm at sample temperatures of 8, 78, and 293 K, representing more than 900 transitions between 24 multiplets L2S+1J of Ho3+(4f10) split by the crystal field, have been analyzed in Czochralski-grown single crystals of Ho3+ doped-yttrium gallium garnet (Y3Ga5O12 or YGG). The Ho3+ ions replace Y3+ ions in sites of D2 symmetry during crystal growth. Associated with each multiplet manifold are 2J+1 nondegenerate crystal-field split sublevels (Stark levels) characterized by one of four different irreducible representations (irreps) associated with D2 symmetry. The energy and irrep assignments for individual experimental Stark levels were established by an algorithm that makes use of the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels. Nearly degenerate Stark levels (quasidoublets) in several manifolds have been observed and investigated by magneto-optical methods reported in a separate study. Of the 252 predicted Stark levels associated with the 24 multiplet manifolds, 241 were experimentally determined of which 161 had symmetry irreps unambiguously identified by the algorithm method and confirmed by crystal-field modeling studies. A final least-squares fitting between 241 calculated-to-experimental Stark levels was obtained with a standard deviation of 4.86 cm−1 (rms error of 4.60 cm−1). The algorithm works best for identifying irreps when neighboring excited Stark levels are sufficiently separated so that a pattern of temperature-dependent (“hot band”) transitions can be unambiguously associated with each excited Stark level.

Spectroscopic and magnetic susceptibility analyses of the 7F J and 5D 4 energy levels of Tb 3+(4f 8) in TbAlO 3

Detailed analyses of spectroscopic and temperature-dependent magnetic susceptibility data are reported for the crystal-field split energy levels of the 7F J and 5D 4 of Tb 3+ in stoichiometric single crystals of ortho-aluminate TbAlO 3. The spectroscopic data include absorption spectra obtained between 2940 and 480 nm from 8 to 300 K. High resolution fluorescence spectra are reported, representing transitions from 5D 4 to 7F 6,5,4, at a sample temperature of 85 K. Using crystal-field modeling techniques recently adapted for low symmetry systems, we have assigned all 58 experimental Stark levels within the 7F J and 5D 4 manifolds, with a fitting standard deviation of 4.5 cm −1 (3.8 cm −1 rms error). As a further test, the theoretical Stark levels and calculated wavefunctions were used to determine the temperature dependence of the magnetic susceptibility along the c-axis of the TbAlO 3 crystal. Good agreement is obtained between the calculated susceptibility and temperature-dependent magnetic data reported earlier, including a prediction of a 0.2 cm −1 splitting of the ground-state quasi-doublet. The susceptibility calculation also confirms the predicted ordering of states within the 7F 6 multiplet manifold.

Crystal field analysis ofPm3+(4f4)andSm3+(4f5)and lattice location studies ofNd147andPm147inw−AlN

We report a detailed crystal field analysis of ${\mathrm{Pm}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ as well as lattice location studies of $^{147}\mathrm{Pm}$ and $^{147}\mathrm{Nd}$ in 2H-aluminum nitride $(w\text{\ensuremath{-}}\mathrm{AlN})$. The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of $60\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. The decay chain of interest in this work is $^{147}\mathrm{Nd}\ensuremath{\rightarrow}^{147}\mathrm{Pm}\ensuremath{\rightarrow}^{147}\mathrm{Sm}$ (stable). Lattice location studies applying the emission channeling technique were carried out using the ${\ensuremath{\beta}}^{\ensuremath{-}}$ particles and conversion electrons emitted in the radioactive decay of $^{147}\mathrm{Nd}\ensuremath{\rightarrow}^{147}\mathrm{Pm}$. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of $873\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ as well as $1373\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The main fraction of about 60% of both $^{147}\mathrm{Pm}$ as well as $^{147}\mathrm{Nd}$ atoms was located on substitutional Al sites in the $\mathrm{AlN}$ lattice; the remainder of the ions were located randomly within the $\mathrm{AlN}$ lattice. Following radioactive decay of $^{147}\mathrm{Nd}$, the cathodoluminescence spectra of ${\mathrm{Pm}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ were obtained between $500\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and $1050\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ at sample temperatures between $12\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. High-resolution emission spectra, representing intra-4$f$ electron transitions, were analyzed to establish the crystal-field splitting of the energy levels of ${\mathrm{Sm}}^{3+}\phantom{\rule{0.3em}{0ex}}(4{f}^{5})$ and ${\mathrm{Pm}}^{3+}\phantom{\rule{0.3em}{0ex}}(4{f}^{4})$ in cationic sites having ${C}_{3v}$ symmetry in the $\mathrm{AlN}$ lattice. Using crystal-field splitting models, we obtained a rms deviation of $6\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ between 31 calculated-to-experimental energy (Stark) levels for ${\mathrm{Sm}}^{3+}$ in $\mathrm{AlN}$. The results are similar to those reported for ${\mathrm{Sm}}^{3+}$ implanted into $\mathrm{GaN}$. Using a set of crystal-field splitting parameters ${B}_{nm},$ for ${\mathrm{Pm}}^{3+}$ derived from the present ${\mathrm{Sm}}^{3+}$ analysis, we calculated the splitting for the $^{5}F_{1}$, $^{5}I_{4}$, and $^{5}I_{5}$ multiplet manifolds in ${\mathrm{Pm}}^{3+}$ and obtained good agreement between the calculated and the experimental Stark levels. Temperature-dependent lifetime measurements are also reported for the emitting levels $^{4}F_{5∕2}\phantom{\rule{0.3em}{0ex}}({\mathrm{Sm}}^{3+})$ and $^{5}F_{1}\phantom{\rule{0.3em}{0ex}}({\mathrm{Pm}}^{3+})$.

On the Use of Ligand Field Parameters in the Study of Coordinated Water Molecules in Eu3+ Complexes

A new methodology is proposed by which the number of coordinated water molecules, n, can be estimated in Eu(3+) complexes. It is based on a comparison between the theoretical and experimental Stark levels, the former being calculated by assuming that n varies from 0 to 4 and predicting the so-called ligand field parameters, . The methodology, initially developed in the study of the Eu(pya)(3).nH(2)O complex, has been applied successfully to beta-diketonate complexes of Eu(3+), for which crystallographic and luminescence data are available.

Absorption spectrum and crystal-field analysis of U4+ ions in CsCdBr3 single crystals

Abstract Single crystals of U4+:CsCdBr3 were grown by the Bridgman–Stockbarger technique. It has been assumed, that U4+ ions are substituting two Cd2+ ions and possess the C3v site symmetry. Thirty seven energy levels, located between 4000 and 25,000 cm−1 and encompassing all but the 1S0 multiplet, were assigned from 7 K absorption spectra. The symmetry of the levels were determined on the basis of the observed small splitting of the Γ3 doublets as well as by a comparison of low temperature absorption spectra of the U4+:CsCdBr3 with that previously reported for U4+ in Cs2UBr6 and Cs2ZrBr6 single crystals. A crystal-field analysis was performed by fitting eight atomic (in the orthogonal formalism) and 6 crystal-field parameters to the experimental Stark levels with an r.m.s. deviation of 100 cm−1. The obtained values of the Hamiltonian parameters are discussed and compared with those reported in previous analyses of U4+ ions. The relatively strong crystal field, resulting in Nv = 8530 cm−1 proves that in the CsCdBr3 crystals the U4+ ions are located at a high symmetry site.

Eu(III) and Gd(III) complexes with pirazyne-2-carboxylic acid: luminescence and modelling of the structure and energy transfer process

The synthesis and spectroscopic study of the complexes of Eu(III) and Gd(III) with pyrazine-2-carboxylic acid (pya) are described. The number of water molecules ( n) in the first coordination sphere of the Eu(III) ion has been determined through comparison between the experimental and theoretical Stark levels, giving n=3, where the geometry of Eu(III) complex has been previously optimised using the Sparkle model. Based on this number of water molecules it has been predicted that the excited states for the complex Eu(pya) 3·3H 2O and the results have been used to carry out an experimental and theoretical analysis of the intensities of the 4f–4f transitions and intramolecular energy transfer processes. Structural data were used to perform theoretical predictions of the Judd–Ofelt intensity parameters ( Ω λ , λ=2,4). The satisfactory results obtained are an indication that the models used can lead to reliable predictions of the structure and 4f–4f intensities. A complete theoretical model to calculate the luminescent properties of lanthanide compounds has been used to analyze the emission quantum yield of the Eu(pya) 3·3H 2O compound. This approach has provided an optimum emission quantum yield of 9.2%.

Crystal-field analysis, upconversion, and excited-state dynamics for(U4+,U3+):Ba2YCl7single crystals

Single crystals of $({\mathrm{U}}^{4+},{\mathrm{U}}^{3+}):{\mathrm{Ba}}_{2}{\mathrm{YCl}}_{7}$ were grown by the Bridgman-Stockbarger technique. The ${\mathrm{U}}^{4+}$ and ${\mathrm{U}}^{3+}$ ions substitute for ${\mathrm{Y}}^{3+}$ and have ${C}_{1}$ site symmetry in ${\mathrm{Ba}}_{2}{\mathrm{YCl}}_{7}.$ Sixty energy levels of ${\mathrm{U}}^{4+}$ were assigned to $40000{\mathrm{cm}}^{\ensuremath{-}1}$ from absorption, excitation, and luminescence spectra, which encompasses all but the ${}^{1}{S}_{0}$ multiplet. A crystal-field analysis was performed by fitting 8 atomic and 19 crystal-field parameters to the experimental Stark levels. The values obtained from the fit had a standard deviation of $36.6{\mathrm{cm}}^{\ensuremath{-}1}$ and agreed with those calculated from the angular overlap model. Efficient luminescence was observed at 7 K from ${\mathrm{the}}^{4}{G}_{7/2}$ and ${}^{4}{F}_{9/2}$ levels of the ${\mathrm{U}}^{3+}$ ions and from the ${}^{1}{D}_{2}$ and ${}^{1}{I}_{6}$ of the ${\mathrm{U}}^{4+}$ ions with decay times of 0.5, 0.55, 9.2, and 4.3 $\ensuremath{\mu}\mathrm{s},$ respectively. For the ${\mathrm{U}}^{4+}$ ions, a very strong anti-Stokes emission was observed due to energy-transfer processes. The emission of the ${\mathrm{U}}^{3+}$ ions is strongly quenched by temperature in contrast to that of the ${\mathrm{U}}^{4+}$ ions for which emission was observed even at room temperature. Energy transfer between the ${\mathrm{U}}^{3+}$ and ${\mathrm{U}}^{4+}$ ions has been shown to occur in the $({\mathrm{U}}^{4+},{\mathrm{U}}^{3+})$ doped ${\mathrm{Ba}}_{2}{\mathrm{YCl}}_{7}.$

Spectra and energy levels of Er3+(4f11) in Gd3Ga5O12

A detailed crystal-field splitting analysis is presented for the energy levels of Er3+(4f11) incorporated into Gd3Ga5O12 single crystals. Spectra are reported between 1600 and 350 nm and were observed at temperatures between 8 K and room temperature. It is most likely that Er3+ ions substitute for Gd3+ ions in cationic sites of D2 symmetry in the cubic garnet host. A parameterized model Hamiltonian including atomic and crystal-field terms is diagonalized over the entire electronic configuration of Er3+(4f11). The diagonalization of the total energy matrix accounts for the intrinsic J–J mixing between states described in terms of the basis set of SLJMJ wave functions. The resolved absorption spectra, representing some 120 transitions from the ground state, I415/2, to excited multiplet manifolds, L2S+1.J, are compared with calculated Stark levels. A final standard deviation of 5.3 cm−1 is obtained between 60 calculated and experimental Stark levels.

Spectroscopic properties of CaF2:U4+ as a saturable absorber

The spectroscopic properties of crystals of CaF2:U4+ have been examined in light of recent interest expressed for this material as a saturable absorber in the passive Q switching of near infrared solid state lasers. The detailed crystal-field splitting of the energy levels of U4+(5f2 ) is analyzed for the ion in different charge-compensated sites. Identification of the site is based on laser excited site-selective spectroscopic studies reported earlier. Experimental Stark levels are compared with calculated levels based on lattice-sum models that include charge compensation in the lattice structure. The final set of atomic parameters for U4+ is in good agreement with values reported for the ion in UF4. The predicted non-Kramers’ doublet as the ground-state Stark level for U4+ in C3V sites is in agreement with the spectroscopic analysis and with results reported earlier from electron spin-resonance studies of CaF2:U4+. Using pump–probe methods, we have investigated excited state absorption (ESA) at 1.54 μm. Consistent with the interpretation of the absorption spectra, we find that the measured ESA is quite small in these crystals. In turn, we use this conclusion to model CaF2:U4+ as a passive Q switch, with good results.

Luminescence properties of Pr3+ and Ce3+ in KCaF3 single crystals

The optical excitation and luminescence spectra of (Pr3+,Ce3+) ions in KCaF3 are presented. High-resolution excitation and emission spectra of Pr3+ and Ce3+ were measured at temperatures between 77 and 293K. First measurements of KCaF3:Ce3+ crystal show that there are nonequivalent Ce3+ centers which radiate either in UV or visible range. The major Ce3+ nonequivalent center in KCaF3 is Ce3+ ion in the site with tetragonal site symmetry (S4). Energy levels for the 4f2 ground configuration of Pr3+ in KCaF3 were established from excitation and fluorescence spectra. Energy levels assignments were made assuming electric-dipole transition selection rules for S4 site symmetry. Twenty-seven energy levels in the lowest six multiplets of the ground configuration were established. In the analysis of experimental data, the Oh magnetic-dipole selection rules were also considered to explain missing or weak transitions which are allowed in S4. Spectra of Pr3+ in KCaF3 have been analyzed with a crystal-field Hamiltonians of S4 or Oh symmetries including J mixing effects. Crystal-field parameters in these Hamiltonians have been determined by the minimization the RMS deviation between calculated and experimental energy Stark levels. We conclude that both model calculations in the S4 and Oh site symmetries for Pr3+ in KCaF3, provide the basis for a consistently good correlation with data.

Optical spectra and thermal Schottky levels in dysprosium sesquisulfide

We report a detailed crystal-field splitting analysis of the energy levels of Dy3+(4f9) in single crystals of Dy2S3 that have the Th3P4 cubic defect structure. From an analysis of the temperature-dependent absorption spectra, we have identified seven of the eight crystal-field split energy (Stark) levels of the ground-state multiplet manifold, H15/26. Sixty-two experimental Stark levels from various multiplet manifolds of Dy3+ are compared with a calculated crystal-field splitting, whose initial crystal-field parameters, Bnm, were determined from lattice-sum calculations. The rms deviation between experimental and calculated levels is 7 cm−1. Both the experimental and calculated crystal-field splitting of the H15/26 manifold are compared with an assignment of Schottky levels obtained from a reassessment of heat capacity data reported earlier. Based on entropy considerations and verification of the Schottky level assignments by analyses of the optical and magnetic susceptibility data, we conclude that the anomaly observed in the heat capacity data near 3.4 K is due to antiferromagnetic ordering.

Infrared-to-visible upconversion inLaCl3:1%Er3+: Energy-level and line-strength calculations

Single crystals of ${\mathrm{LaCl}}_{3}{:1%\mathrm{}\mathrm{Er}}^{3+}$ were grown by the Bridgman technique. ${\mathrm{Er}}^{3+}$ substitutes for ${\mathrm{La}}^{3+}$ and has a site symmetry of ${C}_{3h}$ in ${\mathrm{LaCl}}_{3}.$ Seventy-three energy levels of ${\mathrm{Er}}^{3+}$ were determined up to $45000{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ from absorption, excitation, and luminescence spectra measured over the temperature range 4.2--293 K. A correlated crystal-field analysis was done by fitting 16 atomic, four crystal-field, and one correlated crystal-field parameters to the experimental Stark levels. The fit is excellent with a standard deviation of $9.0{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}.$ On the basis of the wave functions thus obtained the oscillator strengths for the transitions from the ${}^{4}{I}_{15/2}(1)$ ground state to all the levels up to $45000{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ were calculated by fitting seven complex ${A}_{t,p}^{\ensuremath{\lambda}}$ intensity parameters to 47 observed oscillator strengths. The intensity distribution among the crystal-field components was then calculated for the inter-excited-state transition ${}^{4}{I}_{11/2}{\ensuremath{\rightarrow}}^{4}{F}_{7/2}$ which plays an important role in an excited-state-absorption upconversion process.

Site-selective excitation and polarized absorption and emission spectra of trivalent thulium and erbium in strontium fluorapatite

Polarized fluorescence spectra produced by site-selective excitation, and conventional polarized absorption spectra were obtained for Tm3+ and Er3+ ions individually incorporated into single crystals of strontium fluorapatite, Sr5(PO4)3F, also known as SFAP. Substitution of the trivalent rare earth ion for divalent strontium was achieved by passive charge compensation during Czochralski growth of the fluorapatite crystals. Spectra were obtained between 1780 and 345 nm at temperatures from 4 K to room temperature on crystals having the hexagonal structure [P63/m(C6h2)]. The polarized fluorescence spectra due to transitions from multiplet manifolds of Tm3+(4f12), including D21, G41, and H43 to manifolds H63 (the ground-state manifold), F43, H53, H43, and F33 were analyzed for the details of the crystal-field splitting of the manifolds. Fluorescence lifetimes were measured for Tm3+ transitions from D21, G41, and H43 at room temperature and from G41 at 16 K. Results of the analysis indicate that the majority of Tm3+ ions occupy sites having Cs symmetry. A point-charge lattice-sum calculation was made in which the crystal-field components, Anm, were determined assuming that trivalent thulium replaces divalent strontium in the metal site having Cs symmetry. Results support the conclusion that the nearest-neighbor fluoride (F−) is replaced by divalent oxygen (O2−), thus preserving overall charge neutrality and local symmetry. Crystal-field splitting calculations predict energy levels in agreement with results obtained from an analysis of the experimental data. By varying the crystal-field parameters, Bnm, we obtained a rms difference of 7 cm−1 between 43 calculated and experimental Stark levels for Tm3+(4f12) in Tm:SFAP. Absorption and fluorescence spectra are also reported for Er3+ ions in Er:SFAP. Measurement of the temporal decay of the room temperature fluorescence from the I11/24 and I13/24 manifolds yielded fluorescence lifetimes of 230±20 μs and 8.9±0.1 ms, respectively. The experimental Stark levels obtained from an analysis of the spectroscopic data were compared with a crystal-field splitting calculation. The initial set of Bnm parameters for Er3+(4f11) was established from the three-parameter theory and the final set of Bnm parameters obtained for Tm3+(4f12) in Tm:SFAP. The best overall agreement between calculated and experimental Stark levels is 8 cm−1 for 48 Stark levels, representing 12 observed multiplet manifolds of Er3+(4f11) in Er:SFAP.