Order Crystal Field Parameters Research Articles

Judd‐Ofelt analysis and optical properties of Eu3+‐doped GdPO4 phosphors synthesized by combustion method

AbstractThe Eu3+‐doped GdPO4 nanoparticles were prepared via a straightforward combustion method using urea as fuel and nitrates as a precursor. X‐ray powder diffraction patterns, infrared spectrum (IR), HR‐TEM, photoluminescence (PL), phonon sideband and photoluminescence excitation (PLE) were researched. There is a phase transition from the hexagonal phase into the monoclinic phase when the calcined temperature is over 700 °C. All of phosphors have similar morphology and the average diameters for nanoparticles are 20–30 nm. Under the excitation at 273 nm, GdPO4:Eu3+ powders showed red emission bands originating from the 5D0–7FJ (J = 1, 2, 3 and 4) transitions of Eu3+. The orange‐red emission (5D0–7F1 transition) is dominated because the Eu3+ ions exist with inversion symmetry in the lattice. The study suggests that the optimal Eu3+ ions concentration is 5 mol%. In addition, the second order crystal field parameter (B20) and the influence of concentration of Eu3+ ions on decay time are also mentioned, the intensity parameters (Ω2,4,6) and quantum efficiency were determined based on Judd‐Ofelt theory.

Hydrothermally synthesized rod shaped Y2O3:Eu3+ as red emitter

Rod shape Y2O3:Eu3+ were synthesized by using simple hydrothermal method. Characterizations of the samples were done with X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. Increase of Eu3+ concentration in Y2O3 renders shift in Eu – O charge transfer band (CTB) to lower energy. PL emission indicates the asymmetric nature of Eu3+ surroundings. The calculated values of second order crystal field parameter corroborate the asymmetric environment of Eu3+. The improvement in the luminescence with the increase annealing temperature is realized from PL emission and decay lifetime studies. The quantum yield for Y2O3:Eu3+ (13 at.%) under 255 nm excitation is found to be 10 %.

Hydrothermal Synthesis of Rod Shaped Red Emitting Gd2O3:Eu3+ Phosphor.

Simple hydrothermal method can be applied for synthesizing rod shape Gd2O3:Eu3+ phosphors. X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy are used for the characterizations of samples. Increase of Eu3+ concentration in Gd2O3:Eu3+ can cause red shift in the charge transfer band (CTB) of Eu - O. The nature of Eu3+ surroundings is asymmetric. It is ascertained from PL emission studies. The calculation of second order crystal field parameter from PL spectra corroborates the asymmetric environment of Eu3+. PL emission and decay lifetime studies confirm the existence of quenching due cross-relaxation. The quantum yield for Y2O3:Eu3+ (19 at.%) under 265 nm excitation is found to be 7%.

Crystalline electric field study in a putative topologically trivial rare-earth doped YPdBi compound

Topological states of matter have attracted a lot of attention recently due to their intriguing physical properties and potential applications. In particular, the family of half-Heusler compounds (R = rare earth, M = Pt, Pd or Au, and T = Bi, Sb, Pb or Sn) has been predicted to display tunable topological properties via their cubic unit cell volume and/or the charges of the M and T atoms. In this work, we report electron spin resonance (ESR), along with complementary macroscopic experiments, in the putative topologically trivial rare-earth doped (Gd, Nd and Er) YPdBi. From magnetic susceptibility data analysis constrained by ESR results, we were able to extract the fourth (A4) and sixth (A6) order crystal field parameters (CFP) for YPdBi and compared them with those already reported to YPtBi, which is known as a topologically non-trivial compound. We observed that the sign of the CFP changes systematically from YPdBi to YPtBi, possibly due to the inversion of the valence and conduction bands at the Fermi level. The enhanced spin–orbit coupling in YPtBi, when compared to YPdBi, induces the band inversion that drives the system to a non-trivial topological state. This band inversion likely has an effect on the effective charges surrounding the magnetic dopants that are probed by the CFP.

Europium-doped nanocrystalline Y2O3−La2O3 solid solutions with bixbyite structure

Nanocrystals of Y2O3 and La2O3 solid solutions were synthesized with a cubic bixbyite structure containing La2O3 content of up to 50mol%. This is comparatively higher than that in bulk materials of the same structure, where La2O3 content of only 20mol% can be obtained. A set of europium-doped (Y1−xLax)2O3 (x=0.1, 0.2, 0.3, 0.4) cubic bixbyite solid solutions with crystallites of approximately 10nm in size was prepared using the polymer complex solution method. Structural analysis was performed using X-ray diffraction measurements, Rietveld full profile refinement, and from Eu3+ luminescence emission. The energy levels of the Eu3+ ion, second order crystal field parameters, and crystal field strength were obtained for all compositions of solid solutions. We show that the crystal field parameters linearly depend on unit cell parameter and that these dependencies may be considered as part of an overall dependence for the entire sesquioxide family.

Eu3+-doped (Y0.5La0.5)2O3: new nanophosphor with the bixbyite cubic structure

New red sesquioxide phosphor, Eu(3+)doped (Y0.5La0.5)(2)O-3, was synthesized in the form of nanocrystalline powder with excellent structural ordering in cubic bixbyite-type, and with nanoparticle sizes ranging between 10 and 20 nm. Photoluminescence measurements show strong, Eu3+ characteristic, red emission (x = 0.66 and y = 0.34 CIE color coordinates) with an average D-5(0) emission lifetime of about 1.3 ms. Maximum splitting of the F-7(1) manifold of the Eu3+ ion emission behaves in a way directly proportional to the crystal field strength parameter, and experimental results show perfect agreement with theoretical values for pure cubic sesquioxides. This could be used as an indicator of complete dissolution of Y2O3 and La2O3, showing that (Y0.5La0.5)(2)O-3:Eu3+ behaves as a new bixbyite structure oxide, M2O3, where M acts as an ion having average ionic radius of constituting Y3+ and La3+. Emission properties of this new phosphor were documented with detailed assignments of Eu3+ energy levels at 10 K and at room temperature. Second order crystal field parameters were found to be B-20 = -66 cm(-1) and B-22 = -665 cm(-1) at 10 K and B-20 = -78 cm(-1) and B-22 = -602 cm(-1) at room temperature, while for the crystal field strength the value of 1495 cm(-1) was calculated at 10 K and 1355 cm(-1) at room temperature.

Behaviour of electric and magnetic dipole transitions of Eu3+, 5D0 → 7F0 and Eu–O charge transfer band in Li+ co-doped YPO4:Eu3+

The effect of Li+ co-doping on the photoluminescence properties of YPO4:Eu is discussed. Interesting behaviours, such as the presence of intermediate bands, shifting of the Eu–O charge transfer band (Eu–O CTB) to a lower wavelength, variation in intensities of magnetic (5D0 → 7F1) and electric dipole (5D0 → 7F2) transitions of Eu3+ and shift of 5D0 → 7F0 to higher energy with increasing excitation wavelengths are observed. The Eu3+ ion does not have an absorption band in the range 340–350 nm, but after excitation at these wavelengths, a broad emission band (370–570 nm), as well as sharp peaks of Eu3+, could be observed. This is due to strong energy transfer from the intermediate band of the host to the Eu3+ ion. X-ray photoelectron spectroscopy (XPS) study also confirms that intermediate band emission is not due to Eu2+ ion emission. The blue shifting of Eu–O CTB is because of the increase in the optical electronegativity of the Eu3+ ion on Li+ co-doping. The variation in intensities of the 5D0 → 7F2 and 5D0 → 7F1 dipole transitions is related to (i) overlapping interaction parameters within the ground and excited states, (ii) exchange interaction among atoms/ions and (iii) density of the incoming photons. Shift of 5D0 → 7F0 to a higher energy with increasing excitation wavelengths is because of change in the second order crystal field parameter B20 with excitation wavelength. The significant enhancement of luminescence intensity is found with Li+ co-doping due to the increase in crystallinity.

Theoretical Investigation of Energy Levels Splitting of CsCdBr<sub>3</sub>:Pr<sup>3+</sup> Crystal

Based upon the single electron energy state information and the combination of Racah’s group-theoretical consideration with Slater’s wavefunctions, the 91×91 complete energy matrix of 4f2 configuration ion Pr3+ in C3v crystal field has been constructed. The calculated Stark energy levels of CsCdBr3:Pr3+ present a good agreement with the experimental values, which implies that the complete energy matrix method can be received as a recommendable tool to perform a theoretical analysis to the doped crystal. Besides, the influence of Pr3+ ions on the energy levels splitting of the host crystal CsCdBr3 has been compared with two doped trichlorides by Pr3+ ions, which indicates that the sixth order crystal field parameters play an indispensable role in splitting the energy levels.

Exchange and crystal field effects in the ESR spectra ofEu2+inLaB6

Electron spin resonance of ${\mathrm{Eu}}^{2+}$ ($4{f}^{7}$, $S=7∕2$) in a La hexaboride $(\mathrm{La}{\mathrm{B}}_{6})$ single crystal shows a single anisotropic Dysonian resonance. From the observed negative $g$ shift of the resonance, it is inferred that the ${\mathrm{Eu}}^{2+}$ ions are covalent exchange coupled to the $\mathrm{B}\phantom{\rule{0.2em}{0ex}}2p$-like host conduction electrons. From the anisotropy of the spectra (linewidth and field for resonance), we found that the $S$ ground state of ${\mathrm{Eu}}^{2+}$ ions experience a cubic crystal field of a negative fourth order crystal field parameter (CFP), ${b}_{4}=\ensuremath{-}11.5(2.0)\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}$, in agreement with the negative fourth order CFP, ${A}_{4}$, found for the non-$S$ ground state $R$ hexaborides. These results support covalency as the dominant contribution to the fourth order CFP for the whole $R$ hexaboride family.

A spectroscopic investigation of Y 3 Al 5 O 12 :Pr 3 + in translucent ceramic form: Crystal field analysis assisted by configuration-interaction

This paper presents an investigation of Pr3+ doped in the D2 site of Y3Al5O12 (YAG), for the first time on a translucent ceramic sample free of spurious phases, impurity or pair sites. The optical study is carried out by optical absorption, excitation, and emission by selective excitation into 1D2 and 3P0, at different temperatures between 20 K and 60 K, in the 4 300-23 000 cm-1 range. A detailed account of the line assignments is given. 67 over 91 levels of the 4f2 configuration are determined. Several crystal field calculations within the ground configuration 4f2 and the larger matrix 4f2+4f6p are carried out. The energy level fit is slightly improved by configuration interaction. The 3P2 and 1I6 levels are strongly mixed together by the large 6th order crystal field parameters. In sintered samples with different Pr3+ concentrations, satellite lines with intensities increasing quadratically with the concentration are observed. A few weak lines forbidden in D2 site symmetry are observed.

Crystal field study in rare-earth-dopedLuInNi4

Magnetic susceptibility and electron spin resonance experiments in the rare earth $(R=\mathrm{Nd},$ Er, and Yb) $5--25%$ doped cubic intermetallic ${\mathrm{LuInNi}}_{4}$ enable estimates of the fourth ${A}_{4}$ and sixth ${A}_{6}$ order crystal-field parameters for this compound. These parameters yield a ${\ensuremath{\Gamma}}_{6}$ doublet, a ${\ensuremath{\Gamma}}_{7}$ doublet, and a ${\ensuremath{\Gamma}}_{8}$ quartet as the ground states for ${\mathrm{Nd}}^{3+},$ ${\mathrm{Er}}^{3+},$ and ${\mathrm{Yb}}^{3+},$ respectively, and an overall crystal-field splitting of 100--300 K. The ${A}_{4}$ and ${A}_{6}$ parameters are found to have comparable order of magnitude for all the R studied and their values are in agreement with reported values for other cubic systems.

Crystal-field study in rare-earth-doped semiconducting YBiPt

Electron spin resonance (ESR) and magnetic-susceptibility experiments in the rare-earth-doped (R=Nd, Er, and Yb) cubic semiconducting YBiPt allow estimates of the fourth ${(A}_{4})$ and sixth ${(A}_{6})$ order crystal-field parameters for this compound. It is found that these parameters are of the same order for all the R studied. On the other hand, no crystal-field effects were found for the ${\mathrm{Gd}}^{3+}$ doped single-crystal system. Consistent with the small gap semiconducting character of the YBiPt intermetallic compound, a Dysonian ESR line shape with no g shift and Korringa broadening was observed.

Temperature dependence of Faraday rotation and magnetic susceptibility for Ce 3+ and Pr 3+ ions in fluorozirconate glass

The temperature dependencies of the Faraday rotation and magnetic susceptibility for fluorozirconate glass doped with cerium or praseodymium ions are reported. The glass compositions were 52% ZrF 4, 20% BaF 2, 10% CeF 3, 4% AlF 3, and 14% NaF for the cerium-doped glass, and 51% ZrF 4, 21% BaF 2, 8% PrF 3, 4% AlF 3, and 16% NaF for the praseodymium-doped glass; the samples were prepared by quenching from the melt at 1000°C and 960°C for Ce and Pr doped glass, respectively, and annealed at 240°C. Faraday rotations were measured using a modulated optical polarisation technique over a wavelength range of 320–850 nm, and a temperature range of 15–295 K. Magnetic susceptibilities were determined using a transformer-based method over a temperature range of 85–295 K. The paramagnetic part of the Faraday rotation and the magnetic susceptibility both show deviations from Curie's law, and are not simply proportional to each other as frequently assumed. For cerium-doped glass, the temperature dependence of the magnetic susceptibility can be fitted with an expression based on an axially symmetric crystal field appropriate to a square anti-prism site for the cerium ion. The fourth order crystal field parameters are estimated from earlier superposition-model analyses of crystal fields for cerium ions in crystalline fluorides, while the second order parameter is determined by the least squares fitting process.

Magnetic properties of 4f-based intermetallics studied by means of 155Gd Mössbauer spectroscopy

In this report the possibilities to obtain experimental information on various physical properties of rare earth intermetallics by means of 155Gd Mössbauer spectroscopy are reviewed. Results are discussed of compounds related to permanent magnet materials, hydrogen absorbing materials, superconducting and heavy-electron systems. Particular attention is paid to the electric field gradient VZZ and its relation to the second order crystal field parameter A20. Experimental data are compared with results of electronic structure calculations.

155Gd Mössbauer spectroscopy and magnetic properties of several ternary Gd compounds

We have studied the magnetic properties and the 155Gd Mössbauer spectra at 4.2 K of the compounds GdCo 11Ti, GdFe 9Ti 2, GdNi 9In 2, Gd 2Cu 7Al 10, Gd 2RhSi 3 and GdAl 2Ge 2. We have used the experimental values of the electric field gradient at the nuclear Gd site to obtain information on the field gradient experienced at the site of the 4f electrons or equivalently, information on the second order crystal field parameter A 2 0. We have presented examples where the electric field gradient is virtually zero (GdAl 2Ge 2), where it has a distribution centered around zero due to different contributions associated with atomic site disorder (Gd 2Cu 7Al 10), and where two crystallographic inequivalent sites with a markedly different coordination lead to values differing by a factor of about four (Gd 2RhSi 3). We have confirmed the result obtained in a previous investigation that the second order crystal field parameter A 2 0 is positive in RCo 11Ti compounds.

Magnetic incommensurability in hexagonal HoGa2

Specific heat, powder neutron diffraction experiments and magnetization measurements on a single crystal of the hexagonal HoGa2 compound are presented. Below TN = 7.6 K two collinear antiferromagnetic phases (M∥a of the orthohexagonal cell) are observed: (i) a simple collinear antiferromagnetic structure with Q1 =(0, 1, 0) (in the orthohexagonal cell) below Tt = 6.5 K; (ii) a mixing of this phase (about 36%) and of an incommensurate amplitude modulated structure (about 64%) with Q2 =(0.123, 1, 0) for Tt <T <TN. Below TN smooth metamagnetic processes are observed along both directions of the easy basal plane. The second order crystal field parameter A02, deduced from the shift of the reciprocal susceptibilities along and perpendicular to c, is significantly smaller than in the other RGa2 compounds.

Theoretical Calculation of the Crystal Field Parameters of GdCo5, GdFe12, GdFe12N, Gd2Fe17, and Gd2Fe17N3Compounds

The electronic structures of GdCo 5 , GdFe 12 , GdFe 12 N, Gd 2 Fe 17 , and Gd 2 Fe 17 N 3 have been calculated self-consistently by full-potential linearized augmented plane wave method within the framework of the local spin density approximation. The second order crystal field parameters ( A 2 0 ) at Gd-site of these compounds have been determined carefully from the calculated charge distribution. For GdCo 5 , although the calculated value of A 2 0 is larger than experimental ones for SmCo 5 , it is found that the crystal structure is very suitable for producing the large negative value of A 2 0 . For the other compounds, the calculated values of A 2 0 except for GdFe 12 are also larger than experimental ones. The trend of the increase of A 2 0 by introducing nitrogen is, however, in agreement with experimental results. In RFe 11 Ti and R 2 Fe 17 (R=rare earth), the increase of the magnetocrystalline anisotropy energy by introducing nitrogen can be understood from the increase of the asphericity of char...

Magnetization process and site preference of Bi in YIG: Bi epitaxial films studied by 57Fe NMR

The NMR of 57Fe was used to determine the distribution of Bi 3+ ions on the dodechedral sublattice of thin YIG: Bi films with (111) orientation. In a film with 11% Bi 3+ on Y sites the two sublattices which are non-equivalent with respect to the growth direction reveal a difference in the Bi concentration of 10%. The growth induced anisotropy constant was determined from the FMR spectra and allows an estimation of the change of the second order crystal field parameters for the Fe 3+ neighbors of a Bi 3+ ion.

Calculation of spin-reorientation temperature in Nd2Fe14B

The spin-reorientation phenomenon in Nd2Fe14B has been investigated using an angular dependent free energy approach. A magnetic Hamiltonian which includes the crystal electric field term and the exchange term has been established using realistic band structure results. The temperature dependence of the molecular field is accounted for by introducing the Brillouin function and the magnetic Hamiltonian is diagonalized within the ground state multiplet of the Nd ion. The eigenstates are then used to form the partition function for the free energy. At each temperature, the direction of the molecular field is obtained by searching for the minimum in the angular parameter space of the free energy. Our calculations show that for Nd2Fe14B, the net magnetic anisotropy direction is canted away from the c axis at a temperature close to the experimentally reported spin-reorientation temperature of 150 K. The temperature dependence of the magnetic structure is found to be very sensitive to the size of the second order crystal field parameter B20.

Magnetic properties of RIrSi 3 (R = Gd, Dy) from Mössbauer spectroscopy and magnetization measurements

GdIrSi 3 and DyIrSi 3 compounds have been investigated by magnetic susceptibility measurements and by Mössbauer spectroscopy with the 155Gd and 161Dy resonances. Both compounds were shown to order antiferromagnetically at 15.5 and 7.5 K, respectively. The 155Gd Mössbauer data show that the Gd moments are in the basal plane and allow to estimate the leading second order crystal field parameter B 0 2 for the isostructural RIrSi 3 series. It may be anticipated that the easy direction of the magnetization should be parallel to the c-axis when the Stevens factor α J is positive and in the basal when α J is negative (e.g. in DyIrSi 3). The 161Dy Mössbauer data point to the occurrence of an incommensurate modulated spin structure for DyIrSi 3. The reduced average Dy moment of 8.7μ B is attributed to crystal field effects.