New measurements of the emission spectra of Sm2+ in KMgF3 and NaMgF3 crystals

The fluorescence of divalent samarium in KMgF₃ and NaMgF₃ crystals is investigated. The emission is observed to originate from transitions between the ⁵D_J, and ⁷F_J multiplets of the 4?⁶ configuration. More precisely, the lowest ⁵D_J level, ⁵D₀, appears to be the most efficient emitting level in the temperature range 4–300K. Contrary to what has been reported elsewhere, the Sm²⁺ fluorescence in both crystals does not exhibit any broad band emission even at room temperature. The great number of lines in the ⁵D₀→⁷F_J patterns gives evidence of the multiple-center origin of the fluorescence.     

Spectra, energy levels, and symmetry assignments for Stark components of Eu(4f) in gadolinium gallium garnet (Gd3Ga5O12)

Absorption and fluorescence spectra observed between 450 and 750 nm at 85 K and room temperature (300 K) are reported for Eu³⁺(4f⁶) in single-crystal Czochralski-grown garnet, Gd₃Ga₅O₁₂ (GGG). The spectra represent transitions between the ^2S+1L_J multiplets of the 4f⁶ electronic configuration of Eu³⁺ split by the crystal field of the garnet. In absorption, Eu³⁺ transitions are observed from the ground state, ⁷F₀, and the first excited multiplet, ⁷F₁, to multiplet manifolds ⁵D₀, ⁵D₁, and ⁵D₂. The Stark splitting of the ⁷F_J multiplets (J=0-6) was determined by analyzing the fluorescence transitions from ⁵D₀, ⁵D₁, and ⁵D₂ to ⁷F_J. The Eu³⁺ ions replace Gd³⁺ ions in sites of D₂ symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2J+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 D₂ symmetry. The quasi-doublet in ⁵D₁ was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between ⁵D₁ and ⁷F₁. A parameterized Hamiltonian defined to operate within the entire 4f⁶ electronic configuration of Eu³⁺ 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, 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 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 Er³⁺ and Ho³⁺ garnets.     

Influence of J-mixing on the phenomenological interpretation of the Eu3+ ion spectroscopic properties

Two sets of B^k_q crystal field parameters and Bγ_kq intensity parameters have been calculated from the transition occuring between the Stark levels of Eu³⁺ in KY₃F₁₀. One of the calculations includes the J-mixing; the other not. The influence of the J-mixing on the intensities of the “forbidden” transition ⁵D₀ → ⁷F₀ and on the hypersensitive transitions are analysed.     

Crystal field splittings and luminescence properties for Nd3+, Er3+ and Dy3+ in yttrium orthoaluminate (YAlO3)

This report contains information appropriate for a theoretical analysis of the optical spectra of triply ionized lanthanides in YAlO₃. Starting with the best-fit crystal field parameters, the crystal field splitting schemes, multiplet-to-multiplet line strengths, radiative lifetimes, branching ratios, line-to-line square matrix elements and g-factors for the triply ionized Nd, Er and Dy in YAlO₃ have been calculated. In this paper detailed discussions were made on the luminescence properties of the principal transitions of Nd-doped YAlO₃ emanating from the metastable ⁴F_{$\text{3}\text{2}$} state to Stark components of multiplets of the ground ⁴I_J term and compared to similar results of Y₃Al₅O₁₂ (YAG). The line-to-line branching ratios were calculated including J-mixing effects. In the calculations, only electric dipole transitions were considered because of odd-parity. The results predicted some interesting differences in the optical behavior of Nd³⁺ in these two host materials. It has been observed that there is a reasonable agreement between the theoretical data and those reported experimentally for YAlO₃ and YAG. The theoretical studies undertaken here were chosen to supplement or extend the optical data for these two host materials.     

Charge transfer effects on the luminescent properties of Eu3+ in oxysulfides

Energy shifts of 4f⁶ states of Eu³⁺ in matrices, and phonon sidebands, linewidths and luminescence decay of Eu³⁺ in Ln₂O₂S (Ln=Lu, Y, Gd and La) have been studied. The charge transfer state (CTS) of Eu³⁺ is described by a model in which a hole is transferred from Eu³⁺ to ligands. Septet states obtained from the 4f⁷(⁸S) + hole configuration of CTS interact with the ⁷F term of the 4f⁶ configuration. This effect causes downward shifts of ⁷F_J states in matrices. Diffuse charge distributions for ⁷F_J states due to the mixing with CTS make the curvatuve of their adiabatic potential curves be smaller than that for ⁵D_J'. Such a difference in the potential curves between ⁷F_J and ⁵D_J' causes broadening of the absorption lines compared with the corresponding emission linewidths in Y₂O₂S. A dynamic Jahn-Teller model is proposed for the concentration-enhanced phonon sidebands accompanying 4f-4f transitions. The vibronics appear only in the excitation spectra and not in the emission spectra. Spectral distributions of the effective density of phonon states are obtained from the observed phonon sidebands for Ln₂O₂S: 5%Eu. The phonon spectra indicate delocalization of the 4f orbitals of Eu³⁺ with increasing the host-cation radius. The observed lifetimes of ⁵D₀ show a decrease in the same order due to decrease in the 4f-CTS mixing.     

Emission analysis of Tb:MgAl2O4 powder phosphor

This paper reports the emission analysis of green-emitting Tb³⁺-doped MgAl₂O₄ phosphors. Uniformity of the phase of the Tb³⁺-doped MgAl₂O₄ phosphor has been checked by X-ray diffraction (XRD) technique and show common bands existing in the results of Fourier transform infrared (FT-IR). This phosphor exhibits weak blue, orange emissions and a strong emission at λ_exci=350 nm. The blue and green-orange emissions are ascribed to ⁵D₃→⁷F_J and ⁵D₄→⁷F_J (where J=3-6) transitions of Tb³⁺ ions, respectively. These phosphors have shown a strong, more prominent green emission from ⁵D₄→⁷F₅ at 543 nm. The results have indicated that MgAl₂O₄:Tb³⁺ could be a potential candidate as agreen-emitting powder phosphor.     

Spectroscopic and magnetic susceptibility analyses of the FJ and D4 energy levels of Tb(4f) in TbAlO3

Detailed analyses of spectroscopic and temperature-dependent magnetic susceptibility data are reported for the crystal-field split energy levels of the ⁷F_J and ⁵D₄ of Tb³⁺ in stoichiometric single crystals of ortho-aluminate TbAlO₃. 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 ⁵D₄ 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 ⁵D₄ 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 TbAlO₃ 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 ⁷F₆ multiplet manifold.     

The pentad rotation-vibrational states of 12CD4: Wavenumber analysis of infrared and Raman spectra of the ν1, ν3, 2ν2, ν2 + ν4, and 2ν4 bands

The so-called pentad of ¹²CD₄ consists of the vibrational states v₁ = 1(symmetry A₁), v₃ = 1(F₂), v₂ = 2(A₁ + E), v₂ = v₄ = 1(F₁ + F₂), and v₄ = 2(A₁ + E + F₂). All states are located in the 1950 to 2250-cm^?1 region and all are strongly interacting. In the present work we have assigned more than 5000 infrared rotation-vibrational transitions and 163 isotropic Raman transitions from the vibrational ground state to the pentad. We have used infrared and Raman spectra of a resolution better than 0.01 cm^?1. From the experimental wavenumbers 2567 pentad rotation-vibrational energy levels with J ≦ 20 have been determined. These levels are reported in the paper. The levels have been used for refinements of the spectroscopic constants of two physically different effective Hamiltonians for the pentad states. For all levels with J ≦ 12 an unweighted standard deviation of 0.004 cm^?1 is obtained for both Hamiltonians, whereas the standard deviation increases more or less rapidly with J above 12 due to the imperfections of the Hamiltonians. The values of the spectroscopic constants of both Hamiltonians (85 and 106, respectively) are reported and the effects of the approximations are discussed.     

Dependence of photoluminescent properties of cubic Y2O3:Tb nanocrystals on particle size and temperature

Temperature-dependent spectral properties in the cubic Y₂O₃:Tb³⁺ nanocrystals (NCs, 10-70 nm) under 488 nm excitation were studied and compared to that in the bulk. In NCs, emission lines assigned to the ⁵D₄-⁷F_J (J=1-6) transitions of Tb³⁺ ions and a broad band originated from oxygen defects were observed. As a function of temperature, two intensity maximums of the ⁵D₄-Σ⁷F_J transitions appeared in the NCs, at ∼250 and ∼500 K, while in the bulk only one maximum appeared at ∼250 K. The relative intensity of the maximum at ∼500 K to that at ∼250 K increased with decreasing particle size. The intensity maximum of the band emissions that came from the oxygen defects appeared in the range of 500-600 K. The appearance of intensity maximum as a function of temperature was attributed to the rivalry between thermal quenching process and phonon-assisted excitation. The appearance of two maxima in the NCs was attributed to the luminescence contributed by different Tb³⁺ centers, the internal and the surface. The emission for the surface Eu³⁺ centers has higher quenching temperature in contrast to that for the internal centers.     

Fast and efficient VUV/UV emissions from (Ba,La)F2:Er crystals

We report observation of fast and efficient VUV/UV luminescence from the mixed (Ba,La)F₂:Er crystals. The broad bands, peaking at 162.5, 181.9, 194.2, 202.8, 216.1, 233.5 and 281.5 nm and decaying, at 10 and 293 K, with time constants of 46 and 35 ns respectively, are due to spin-allowed transitions from the low-spin (LS) state of the 4f¹⁰5d configuration.We also observed a weak and slow broad band emission peaking at 170 nm due to the spin-forbidden transition from the high-spin (HS) state of the 4f¹⁰5d configuration.While at room temperature the excitation into any of the three identified LS bands (J=8, 7 and 6) dominating the excitation spectrum yields fast VUV and UV emissions, at 10 K the excitation into higher lying J=7 and 6 bands generates slow and sharp line emissions. The positions of these lines fit energies of transitions originating from the ²G_7/2 multiplet at 66140 cm⁻¹. The emission from the ²G_7/2 multiplet has been never, to the best of our knowledge, observed before.The efficient and fast VUV and UV emissions from the higher (LS, J=8) with almost no contribution from the lower (HS, J=8) level of the 4f¹⁰5d configuration are possible because the modified crystal field in (Ba,La)F₂ shifts the level of the (LS, J=8) state below the ²F_5/2 multiplet which, therefore, does not contribute to nonradiative relaxation between the LS and HS levels.We conclude that the ²G_7/2 and ²F_5/2 levels have major impact on VUV and UV emissions from the Er³⁺ ion in (Ba,La)F₂ contributing to complex emission pattern described in this report Their key role, elucidated by the VUV and UV luminescence spectroscopy, is consistent with predictions from a simple configuration coordinate model based on experimental results and calculations of the 4f¹¹ energy levels.     

Comparative structural and photoluminescent study of Eu-doped La2O3 and La(OH)3 nanocrystalline powders

Eu³⁺-doped La₂O₃ nanocrystalline powder was prepared by polymer complex solution method and further used for preparation of Eu³⁺-doped La(OH)₃. Structural and optical characterization was carried out by powder X-ray diffraction and photoluminescent spectroscopy. XRD measurements confirmed the formation of hexagonal La₂O₃ and its recrystallization into La(OH)₃ in a humid atmosphere. Excitation spectra show redshift of host lattice and charge transfer emission bands in La(OH)₃ while bands that correspond to Eu³⁺f–f transitions are placed at same wavelengths in both samples. Photoluminescence spectra recorded over the temperature range from 10 K to 300 K show that intensities of emission lines in Eu³⁺-doped La₂O₃ do not depend on temperature as much as in La(OH)₃ sample. Observed dominant ⁵D₀→⁷F₂ and markedly visible ⁵D₀→⁷F₀ emissions in doped La₂O₃ indicate that Eu³⁺ ion is located in a structural site without an inversion center. On the other hand, in Eu³⁺-doped La(OH)₃⁵D₀→⁷F₀ transition is barely visible while ⁵D₀→⁷F₂ is not prominent, and with temperature drop three ⁵D₀→⁷F_J (J=1, 2, 4) transitions become almost of the same intensity. In both La₂O₃ and La(OH)₃ structures Eu³⁺ ion replaces La³⁺ in non-centrosymmetric C_3v and C_3h crystallographic sites, respectively, and difference in symmetry of the crystal field around europium ion is explained by comparing shape and volume of these sites. Decay times of the ⁵D₀- level recorded over the temperature range 10−300 K revealed that emission lifetime values in La₂O₃ (~0.7 ms) are almost two times higher than in La(OH)₃ (~0.4 ms), and unlike in La₂O₃, lifetime in La(OH)₃ is temperature dependent.     

Upconversion luminescence in Yb/Tb-codoped monodisperse NaYF4 nanocrystals

Upconversion (UC) luminescence in monodisperse NaYF₄:Yb³⁺/Tb³⁺ nanocrystals was observed under diode laser excitation of 970 nm, which were synthesized by a hydrothermal method. UC emissions at 380, 413, 436 nm and at 488, 542, 584, 620 nm arise from transitions ⁵D₃(⁵G₆) → ⁷F_J(J = 6, 5, 4) and ⁵D₄ → ⁷F_J(J = 6, 5, 4, 3) of Tb³⁺ ions, respectively. UC mechanisms are proposed based on spectral, kinetic, decay time measurements, and pump power dependence analyses. Blue, green and red emissions originate from the same long-lived (milliseconds) upper ⁵D₄ state, which promises the potential applications of these monodisperse Yb³⁺/Tb³⁺-codoped NaYF₄ nanocrystals in the field of photonics, lasers and biomedicine.     

Laser Stark spectroscopy of the ν4 band of CH3C15N: Fermi resonance with 3ν83

Laser Stark spectra for the ν₄ band of CH₃C¹⁵N have been measured by using CO₂ and N₂O lasers. Almost 650 resonances have been assigned to about 140 ro-vibrational transitions with J′ ≤ 34 and K ≤ 11. An anomaly of the rotational structure around K = 7 has been proved to be due to a Fermi interaction by analyzing each K subband separately. Observed data have been fitted to a model which includes ν₄-3ν₈³ Fermi coupling by the method of least squares. The standard deviation of observed from calculated frequencies is 4.6 MHz. Molecular constants derived are also listed.     

A potential reddish orange emitting phosphor Ca2BO3Cl:Eu for white light-emitting diodes

A series of phosphors Ca₂BO₃Cl:Eu³⁺ were synthesized by using a high-temperature solid-state reaction technique, and their UV–vis luminescence properties were investigated. The f–f transitions of Eu³⁺ in the host lattice were assigned and discussed. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (394 nm), and exhibit reddish orange emission corresponding to the ⁵D₀→⁷F_J (J=0, 1, 2) transitions of Eu³⁺. The influence of the doping concentration and charge compensators on the relative emission intensity of Eu³⁺ was investigated, and the optimum doping concentration is 0.04. The critical distance R_c was estimated to be 17.1 Å in terms of the concentration quenching data. The present study suggests that Ca₂BO₃Cl:Eu³⁺ can be a potential candidate as an UV-convertible phosphor for white light-emitting diodes (LEDs).     

N2-broadening coefficients in the ν2 and ν4 bands of PH3

N₂-broadening coefficients are measured for 61 transitions of PH₃ in the ^QR branch of the ν₂ band and the ^PP, ^RP, ^SP, and ^PQ branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 1 to 16 and K from 0 to 11 are located between 1008 and 1106 cm⁻¹. The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter models provide larger broadening coefficients than the Voigt model. These coefficients have also been calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to the electrostatic contributions. The theoretical results are in good agreement with the experimental data and reproduce the J dependence of the broadenings, but their decrease at high J values is overestimated for the ^QR (J, K) transitions.     

On the 5D0→7F0 transition of the Eu3+ ion in the {(C4H9)4N}3Y(NCS)6 host

In this article we apply a model, based on the combined effect of a polarizable chemical environment (the Pseudo-Multipolar Field) and the mixing between J-levels, to study the ⁵D₀→⁷F₀ intensity of the Eu³⁺ ion in the {(C₄H₉)₄N}₃Y(NCS)₆ host. Good agreement is found between theory and experiment. The results are discussed.     

Effects of Tb doping on the photoluminescence of Y2O3:Tb nanophosphors

The effects of Tb doping on the photoluminescence (PL) of Y₂O₃:Tb nanophosphors have been investigated. Nanophosphors were prepared by the glycine-nitrate solution combustion technique using yttria and terbia powders as precursors. PL excitation spectra at room temperature consist of two overlapping bands centered at 277 and 304 nm, whereas emission spectra comprise several groups of lines corresponding to the ⁵D₄→⁷F_J (J=1-6) 4f electronic transitions of the Tb⁺³ ions. A direct comparison of nanophosphor and bulk concentration-quenching curves was obtained by annealing the nanophosphor powder and converting it to bulk material without altering the Tb concentration. The peak in the nanophosphor concentration-quenching curve occurs at a concentration ∼3 times higher than that of the bulk.     

Luminescence properties of novel NaBa4(BO3)3:Ce, Eu phosphors

Novel Eu³⁺, Ce³⁺ activated NaBa₄(BO₃)₃ phosphors were synthesized by solid-state reactions. The excitation spectrum of NaBa₄(BO₃)₃:Ce³⁺ consists of an intense band peaking at 350 nm and a weak band in the higher energy side, and the emission spectrum exhibits a blue band with a maximum at about 420 nm. The Eu³⁺ emission in NaBa₄(BO₃)₃ consists of the transitions from ⁵D₀ to ⁷F_J, and the excitation spectrum consists of broad excitation band peaking at 270 nm and some intense narrow lines. The optimum doped concentration, the critical distance of the concentration quenching, and the fluorescence lifetime have also been investigated.     

Synthesis and luminescence properties of europium doped YBa3B9O18

Europium (Eu³⁺) doped YBa₃B₉O₁₈ were synthesized by conventional solid state solidification methods. (Y_1−xEu_x)Ba₃B₉O₁₈ formed solid solutions in the range of x=0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu³⁺ excitation and emission. The charge transfer excitation band of Eu³⁺ dominates the excitation spectra. The emission spectrum of Eu³⁺ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the ⁵D₀ level to the levels ⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions. The dependence of luminescence intensity on Eu³⁺ concentration shows no concentration quenching for fully concentrated EuBa₃B₉O₁₈. Eu³⁺ doped YBa₃B₉O₁₈ are promising phosphors for applications in displays and optical devices.     

Structure and visible photoluminescence of Sm3+, Dy3+ and Tm3+ doped c-axis oriented AlN films

Visible photoluminescence (PL) has been observed from rare earth (Tm, Sm and Dy)-doped AlN films grown by radio-frequency magnetron reactive sputtering. X-ray diffraction indicates that the films are c-axis-oriented hexagonal wurtzite type structure with an average crystal size of about 80--110nm. Room-temperature PL spectra indicate that the blue emission is due to the transition of ¹D₂ to ³F₄ and ¹G₂ to ³H₆ intra 4f electron of Tm³⁺, the yellow emissions of AlN:Sm are due to ⁴G_5/2 to the ⁶H_J (J = 5/2, 7/2, 9/2, 11/2) and the reddish emissions of AlN:Dy correspond to the ⁴F_9/2 to ⁶H_J (J = 15/2, 13/2, 11/2 and 9/2) and ⁶F_11/2 transitions.