Comparative analysis of energy-level splitting of Pr3＋ doped in LiYF4 and LiBiF4 crystals： a complete energy matrix calculation

Based on the combination of Racah's group-theoretical consideration with Slater's wavefunction, a 91 × 91 complete energy matrix is established in tetragonal ligand field D_2d for Pr³⁺ ion. Thus, the Stark energy-levels of Pr³⁺ ions doped separately in LiYF₄ and LiBiF₄ crystals are calculated, and our calculations imply that the complete energy matrix method can be used as an effective tool to calculate the energy-levels of the systems doped by rare earth ions. Besides, the influence of Pr³⁺ on energy-level splitting is investigated, and the similarities and the differences between the two doped crystals are demonstrated in detail by comparing their several pairs of curves and crystal field strength quantities. We see that the energy splitting patterns are similar and the crystal field interaction of LiYF₄:Pr³⁺ is stronger than that of LiBiF₄:Pr³⁺.     

Luminescence of Pr3+-Activated fluorides

The strong dependence of the emission spectrum of YF₃:Pr³⁺ on excitation source (228.8 nm, 213.9 nm or cathode rays) is ascribed to two different types of Pr³⁺ sites: one with a relatively strong crystal field and the other with a relatively weak crystal field. The presence of the latter is connected with the conversion of one short-wave UV (? 215 nm) photon into two visible photons. Two-photon luminescence of Pr³⁺ was also found for α-NaYF₄ and LaF₃, but not for CaF₂ and BaF₂ due to the too strong crystal field in these lattices. The occurrence of two-photon Pr³⁺ luminescence is compared with the intensity of the IR-excited green emission of the corresponding Yb³⁺, Er³⁺-activated lattices. The intensity of the Pr³⁺ luminescence at shortwave UV excitation (213.9 nm) is rather weak. Luminescence of reasonable efficiency is, however, observed on excitation with cathode rays.     

Luminescence of Cs2NaScCl6:Pr3+: Effects of Changing the Elpasolite Lattice Parameter

Abstract

The luminescence spectrum of Cs₂NaScCl₆:Pr³⁺ (0.1 at.%) has been recorded at temperatures down to 10 K and assigned between 20,800 and 9900 cm^?1. Twenty‐three energy levels of the 4f² configuration Pr³⁺ ion were located and then fitted by the conventional 4f² crystal field calculation, as well as by a configuration interaction assisted crystal field (CIACF) calculation. The latter gave a much better fit. A comparison of the fit for Cs₂NaScCl₆:Pr³⁺ with fits upon the same set of energy levels in Cs₂NaYCl₆:Pr³⁺ and Cs₂NaPrCl₆, where the fifth nearest neighbor of Pr³⁺ is changed and the lattice parameter increases along this series, shows a decrease in the magnitudes of the crystal field parameters, which were also semiquantitatively simulated. Several facets of the emission spectra are interesting, including the observation of weak progressions in the totally symmetric Pr–Cl stretching vibration and the occurrences of the resonance of electronic and vibronic states. The spectra of Cs₂NaScCl₆:Pr³⁺ (1 at.%) differ considerably from those of the more dilute system and show that other species are formed rather than a complete substitution of the Sc³⁺ sites by Pr³⁺.     

Tysonite structure and crystal-field analysis of the Pr3+ ion in PrF3

The quadratic Zeeman effect of the Pr³⁺ ion in PrF₃ and a Raman spectroscopic investigation of the optical phonons in LaF₃ have been used to test the crystal structures proposed in the past for tysonite. We find that the twinned structure is consistent with all available experimental results. A crystal field Hamiltonian parametrized in monoclinic symmetry was used to describe the observed crystal field splittings of Pr³⁺ in PrF₃. Our best parameter set gave a r.m.s.-deviation of 12 cm^–1. As a test for the eigenfunctions the quadratic Zeeman shifts are calculated and compared with the experimental results.     

On the correlation between the composition of Pr doped garnet type materials and their photoluminescence properties

Lu₃(Al,Ga)₅O₁₂ and (Y,Lu)₃(Al,Mg,Si)₅O₁₂ samples doped with 1% Pr³⁺ were prepared by two aqueous sol-gel chemistry approaches, such as citrate and glycolate methods. All samples were characterised by powder X-ray diffraction (XRD), thermal quenching (TQ), fluorescence lifetime measurements and photoluminescence (PL) techniques. It turned out that the Pr³⁺ emission is very sensitive to the composition of the garnet host lattice. Lu₃Al₅O₁₂:Pr³⁺ samples showed mainly [Xe]4f¹5d¹→[Xe]4f² broad band emission in UV-blue region, whereas [Xe]4f²-[Xe]4f² line emission of Pr³⁺ dominated in Lu₃Ga₅O₁₂ samples. Modification of garnet crystals with Mg²⁺-Si⁴⁺ pair has led to generation of strong crystal field strength resulting in energy transfer from 5d to 4f orbitals. Y₃AlMg₂Si₂O₁₂ composition generated the strongest crystal field splitting out of all synthesised samples and showed practically only Pr³⁺ [Xe]4f²-[Xe]4f² line emission in the red spectral region.     

Magnetic interactions in Pr3+ : LiYF4 for quantum manipulation : search for an efficient three-level Λ system

The influence of an external magnetic field on the hyperfine structure of the ³ H₄(0) and ¹D₂(0) crystal field states of Pr³⁺ in LiYF₄ is studied in order to find an efficient three-level Λ system. Using an experimentally determined spin Hamiltonian, we show that three-level Λ systems can be obtained with equal strengths for the optically excited transitions under various magnetic field magnitudes and orientations. An analytical analysis based on two levels is proposed to find useful magnetic fields without extensive numerical calculations and to understand the general behaviour of the system. Pr³⁺ hyperfine structure has also been directly calculated using a complete Hamiltonian including free ion, crystal field and magnetic interactions. A good agreement with the spin Hamiltonian approach is found for the ground state whereas the excited state results poorly reproduce the experiment. This is attributed to the low accuracy of ¹D₂ crystal field wavefunctions. This suggests that transition strengths ratios could be calculated directly from the crystal field Hamiltonian with improved crystal field parameters.     

EPR spectrum of gadolinium in hydrated praseodymium sulphate

The electron paramagnetic resonance of Gd³⁺ in single crystal of Pr₂(SO₄)₃.8H₂O is studied at room temperature. Two magnetic complexes exhibiting orthorhombic or lower symmetry are found and the results have been fitted to a suitable spin Hamiltonian. The exact solution of Hamiltonian matrix is carried out and 10 “best fit” parameters are obtained using iterative optimization technique. The zero field splittings of Gd³⁺: Pr₂(SO₄)₃.8H₂O have been computed. Few forbidden transitions are observed and explained using numerical solution of the Hamiltonian matrix.     

Laser excitation of Pr3+ sites in ThCl4:Pr3+

Use of site selection spectroscopic techniques combined with low temperature absorption spectral studies has enabled the identification and characterization of ten optically important charge-compensated crystallographic sites for Pr³⁺ in the β-ThCl₄:Pr³⁺ system. Fluorescence decay time measurements, variation of site distribution with dopant concentration and fluorescence spectra were used to characterize the sites. Distant charge compensation is found to be one of the dominant modes of charge compensation of Pr³⁺ in ThCl₄, and its predominance over other sites increases as Pr³⁺ concentration decreases. The sinusoidal distortion of the crystal field symmetry around Pr³⁺ in the incommensurate phase of β-ThCl₄ is believed to be mainly responsible for the splitting and continuous shift in fluorescence spectral lines which occur when ³P₀→³F₂ fluorescence scans are made with excitation at different points on the ³P₀←³H₄ absorption line belonging to different sites.     

Crystal field splitting of Pr3+ in PrAl2 investigated by inelastic neutron scattering

We report the.results of an experimental determination of the crystal field splitting of Pr³⁺ in PrAl₂ by means of inelastic neutron scattering. For the crystal field parameters we obtain B₄ = (47.2 ± 4.0) × 10^?4 meV and B₆ = ? (156 ± 12) × 10^?6 meV.     

Absorption and emission spectra of yttria-stabilized zirconia and magnesium oxide

We have investigated the luminescence and absorption spectra of doped and undoped ZrO₂-Y₂O₃ and MgO crystals at room- and low temperatures. The crystals used are partly doped with the transition metals Ni, Co, Cr and the rare earth Pr. The emission spectra were obtained under laser excitation at different wavelengths. The observed optical emission and absorption bands of the MgO crystals doped with Ni, Co and Cr correspond to transitions between spin-orbit split crystal field levels of the transition metals. Luminescence and absorption bands of undoped yttria-stabilized zirconia (YSZ) crystals are due to color centers, absorption bands of the doped YSZ correspond to the well known transitions of the Ni²⁺, Co²⁺ and Pr³⁺ ions, respectively. The emission spectra of the doped YSZ obtained under various laser excitations can be explained by an energy transfer process between the color center and the doping materials. The influence of annealing on the absorption and emission of Pr³⁺/Pr⁴⁺ is investigated.     

Up-conversion multiwave (White) luminescence in the visible spectral range under excitation by IR laser diodes in the active BaY2F8:Yb3+,Pr3+ medium

The possibilities of occupying high-lying 4f states of Pr³⁺ ions in the active BaY₂F₈:Yb³⁺,Pr³⁺ medium according to the photon avalanche and step-by-step sensitization mechanisms are compared. It is shown that the photon avalanche is unlikely to occur in the BaY₂F₈:Yb³⁺,Pr³⁺ crystal. The multiband luminescence spectra in the visible spectral range (white emission) under single- and multiwave pumping of BaY₂F₈:Yb³⁺,Pr³⁺ crystal by IR laser diodes are reported.     

Optic characteristics of Pr3+ doped NaY(MoO4)2 crystal

The polarized absorption and emission spectra of Pr³⁺ ions in NaY(MoO₄)₂ single crystal were investigated. The standard and modified Judd–Ofelt theory have been applied to the measured optical absorption intensities to determine the spectroscopic parameters, including the Judd–Oflet intensity parameters Ω_t (t=2,4,6), the radiative transition rates, branching ratios, and emission cross-sections for various excited levels of Pr³⁺ ions. In samples with Pr³⁺ ions concentration of 2.00×10²⁰ cm^-3, the excitation of the ¹ D ₂ manifold decays non-radiatively by the electric dipole–dipole transfer between Pr³⁺ neighbors. The good spectroscopic properties show the possible application of the Pr³⁺ doped NaY(MoO₄)₂ crystal as a solid-state laser. PACS 42.70.Hj; 78.20.-e     

Spectral-kinetic characteristics of Pr luminescence in LiLuF4 host upon excitation in the UV-VUV range

Spectral-kinetic study of Pr³⁺ luminescence has been performed for LiLuF₄:Pr(0.1 mol%) single crystal upon the excitation within 5-12 eV range at T=8 K. The fine-structure of Pr³⁺ 4f ²→4f 5d excitation spectra is shown for LiLuF₄:Pr(0.1 mol%) to be affected by the efficient absorption transitions of Pr³⁺ ions into 4f 5d involving 4f ¹ core in the ground state. Favourable conditions have been revealed in LiLuF₄:Pr(0.1 mol%) for the transformation of UV-VUV excitation quanta into the visible range. Lightly doped LiLuF₄:Pr crystals are considered as the promising luminescent materials possessing the efficient Pr³⁺³P₀ visible emission upon UV-VUV excitation. The mechanism of energy transfer between Lu³⁺ host ion and Pr³⁺ impurity is discussed.     

Spectroscopic properties of Pr:KY(MoO4)2 crystal as a visible laser gain medium

A Pr³⁺-doped KY(MoO₄)₂ single crystal was grown by the Czochralski method. The polarized absorption and fluorescence spectra of the Pr³⁺:KY(MoO₄)₂ crystal were measured at room temperature. The stimulated emission cross-sections for the transitions from the ³P₀ multiplet were estimated from the fluorescence spectra. The fluorescence lifetime of the ³P₀ multiplet was estimated from the fluorescence decay curve at room temperature. The analysis of spectral properties shows that the Pr³⁺:KY(MoO₄)₂ crystal is a promising gain medium for visible lasers.     

Infrared study in high magnetic fields of the crystal-field excitations in PrMnO3

Pr³⁺ ion crystal field (CF) excitations in PrMnO₃ single crystals have been studied by infrared transmission, in the 1800–8000 cm⁻¹ range, as a function of temperature and applied magnetic field up to 13 T. No noticeable frequency shifts which might occur below T_N∼100 K, as a result of the antiferromagnetic transition, are observed in the Pr³⁺ CF levels. A set of CF parameters that fit the experimental levels as well as the low temperature Pr³⁺ magnetic moment in PrMnO₃ has been determined.     

Crystal fields of Pr in LiYF4 under pressure

Fluorescence spectra of LiYF₄:Pr³⁺ have been measured between 12,000 and 22,000 cm⁻¹ under pressures up to 10 GPa. In total, 25 crystal field energy levels were obtained and used for the determination of free-ion and crystal field parameters under pressure. According to the nephelauxetic effect, the free-ion parameters decrease with increasing pressure. The relative decrease is larger for the Slater than for the spin-orbit coupling parameter. This behavior is consistent with former studies on Pr³⁺ in different crystals and can be explained by a special covalency model. According to an effective D_2d symmetry, five crystal field parameters B₀²(f,f), B₀⁴(f,f), B₄⁴(f,f), B₀⁶(f,f), and B₄⁶(f,f) are non-zero. The pressure-induced changes of these parameters have been determined up to the maximum pressure of 10 GPa. In order to improve the calculation of the crystal field levels, the configuration interactions with the 4f¹6p¹ configuration have been taken into account. The effect of these interactions are also analyzed under pressure and distinct improvements of the energy level calculations have been obtained.     

Spectroscopic characteristics of Pr<Superscript>3+</Superscript> in biaxial La<Subscript>2</Subscript>(WO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystal

A Pr³⁺-doped La₂(WO₄)₃ crystal grown by the Czochralski method has been investigated as a promising laser material. The principal axes of the optical indicatrix and Pr³⁺ concentration of the crystal were determined. The polarized absorption, fluorescence spectra and fluorescence decay curves of the main emission multiplets of the crystal were measured at room temperature. The spectroscopic parameters were obtained by the modified Judd–Ofelt theory combined with the normalized method. The peak stimulated emission cross-sections of the major emission lines were estimated. The good spectroscopic properties imply that the Pr³⁺:La₂(WO₄)₃ crystal is a potential laser gain medium for solid-state laser and self-stimulated Raman laser applications. PACS 78.20.-e; 42.70.Hj     

Ce and Pr5d-energy levels in the (pseudo) perovskites KMgF3 and NaMgF3

The location of the 5d-energy levels of Ce³⁺ and Pr³⁺ in the cubic perovskite KMgF₃ and in the distorted perovskite NaMgF₃ was determined from spectroscopic studies in the vacuum ultraviolet. It is established that Ce³⁺ and Pr³⁺ ions both occupy the same site in each host: K⁺ sites for KMgF₃ and Na⁺ sites for NaMgF₃. The small crystal field splitting and the small value of the centroid shift of the 4fⁿ⁻¹5d-configuration yield a relatively high energy for the lowest 5d state of both Ce³⁺ and Pr³⁺. The lowest 5d state of Pr³⁺ in both hosts is found at energy higher than the 4f² state, enabling the photon cascade emission to occur.     

Neutron spectroscopy of 0.6 meV crystal field transitions in doped superconductors

Transitions between the low lying crystal field states of Tb³⁺ and Pr³⁺ substituted for La in the superconductors LaAl₂, LaAg, and LaSn₃ have been observed by inelastic neutron scattering. Level separations of less than 1 meV and linewidths could be measured for concentrations as small as 2 mole %.     

The laser-diode-excited 5d-4f luminescence of Ce3+ and Pr3+ ions embedded into a BaR2F8 matrix

We show the possibility of obtaining UV luminescence from 5d-4f transitions of rare-earth ions in the BaY₂F₈: (Yb³⁺, Pr³⁺, Ce³⁺) crystal under upconversion excitation by standard laser diodes with lasing wavelengths of 960, 808, and 840 nm. Various upconversion mechanisms of pumping for populating the higher-lying energy levels of the active ions, as well as methods of adaptation of the active medium BaY₂F₈: (Yb³⁺, Pr³⁺, Ce³⁺) to these mechanisms, are considered.