Synthesis and characterization of fast-decaying bluish green phosphors of Tb3+-doped CaSi2O2N2 for 2D/3D plasma display panels

Oxynitride phosphor powders comprising of CaSi₂O₂N₂ doped with Tb³⁺ were successfully synthesized using a high-temperature solid-state reaction method. The experimentally determined photoluminescence (PL) properties of the produced phosphors meet the requirements of 2D/3D plasma display panels (PDPs). In particular, under the excitation of vacuum ultraviolet (VUV) synchrotron radiation and ultraviolet (UV) irradiation, emission peaks corresponding to the ⁵D₃→⁷F_J (J=6, 5, 4, 3) and ⁵D₄→⁷F_J (J=6, 5, 4, 3) transitions of Tb³⁺ ions were recorded. Monitoring the ⁵D₄→⁷F₅ emission of Tb³⁺ at 545 nm, the excitation bands were assigned to the host-related absorption as well as the 4f–5d (fd) and the 4f–4f (ff) transitions of Tb³⁺. The produced phosphors can be efficiently excited at 147 nm, and have an adequately short decay time (τ_1/10=1.14 ms).     

Green emission from Tb-doped SrSi2O2N2 phosphors under ultraviolet light irradiation

Tb-doped SrSi₂O₂N₂ phosphors with promising luminescent properties were synthesized by the conventional solid-state reaction method, characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. The synthesized materials exhibited a weak blue emission and a strong green emission in the region of 400-470 nm and 480-650 nm, which are attributed to ⁵D₃→⁷F_j (j=5, 4, 3) and ⁵D₄→⁷F_j (j=6, 5, 4, 3) transitions of Tb³⁺, respectively. The green emission from ⁵D₄→⁷F₅ at 543 nm showed the highest intensity under the optimized concentration of 0.1 mol, after which the quenching concentration became relevant. The quenching behavior of the emission of Tb³⁺ was explained by the cross-relaxation of its excited state.     

Rotational and hyperfine spectra for a sandwich titanium complex, C5H5TiC7H7

Microwave spectroscopy measurements and density functional theory calculations are reported for the cyclopentadienyl cycloheptatrienyl titanium complex, C₅H₅TiC₇H₇. Rotational transition frequencies for this symmetric-top complex were measured in the 4-13 GHz range using a Flygare-Balle-type pulsed beam spectrometer. The spectroscopic constants obtained for the normal C₅H₅⁴⁸TiC₇H₇ isotopomer are B = 771.78907(38), D_J = 0.0000295(41), and D_JK = 0.001584(73) MHz. The quadrupole hyperfine splittings for C₅H₅⁴⁷TiC₇H₇ were clearly observed and the measured constants are B = 771.79024(32) MHz, D_J = 0.0000395(33), D_JK = 0.001646(24), and eQq_aa = 8.193(40) MHz. Analysis of the experimental and theoretical rotational constants indicates that the η⁷-C₇H₇Ti and η⁵-C₅H₅Ti bond lengths in the gas phase are about 0.02 Å longer than those reported for the solid-state X-ray structure. The calculated Ti-C bond lengths are shorter for the C₇H₇ ligand (r(Ti-C) = 2.21 Å) than for the C₅H₅ ligand (r(Ti-C) = 2.34 Å), and the C₇H₇ H atoms are displaced 0.15 Å out of the C₇ plane, toward the Ti atom.     

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.     

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.     

红色LiMBO3 : Re3+(Re=Eu,Sm) 发光材料的特性

采用固相法制备了红色LiM(M=Ca, Sr, Ba)BO₃ : Re³⁺(Re=Eu, Sm)发光材料,研究了材料的发光性能。研究发现LiM(M=Ca, Sr, Ba)BO₃ : Eu³⁺材料呈现多峰发射,最强发射分别位于610,615,613 nm处,分别监测这三个最强峰,所得激发光谱峰值位于369,400,470 nm。LiM(M=Ca, Sr, Ba)BO₃ : Sm³⁺材料也呈多峰发射,分别对应Sm³⁺的⁴G_5/2→⁶H_5/2、⁴G_5/2→⁶H_7/2和⁴G_5/2→⁶H_9/2跃迁发射;分别监测602,599,597 nm三个最强发射峰,所得激发光谱峰值位于374,405 nm。研究了激活剂浓度对材料发射强度的影响,结果随激活剂浓度的增大,发射强度先增强后减弱,即,存在浓度猝灭效应。实验表明,加入电荷补偿剂Li⁺、Na⁺或K⁺均可提高LiM(M=Ca, Sr, Ba)BO₃ : Re³⁺(Re=Eu, Sm)材料的发射强度。     

VUV-UV luminescence of magnetoplumbite: (Sr0.96−xBa0.04)Al12−yMgyO19:Tbx

The title compounds (Sr_0.96−xBa_0.04)Al_12−yMg_yO₁₉:Tb_x (0<x<0.4; 0<y<0.18) are single-phase magnetoplumbite determined by X-ray powder diffraction analysis. The characteristic emission lines of ⁵D₃→⁷F_j (j=2, 3, 4, 5) and ⁵D₄→⁷F_j (j=4, 5, 6) of Tb³⁺ are recorded under the VUV excitation. The intensive luminescence mainly comes from ⁵D₃→⁷F_j transition when the concentration of Tb³⁺ is low. However, when the concentration of Tb³⁺ starts to increase from very low concentration, ⁵D₄→⁷F_j transition is becoming dominant. Three broad excitation bands at 165, 193 and 233 nm have been observed. The band at 165 nm originates from the overlap between the host absorption and the charge transfer of Tb³⁺-O²⁻. The other two broad bands are the first spin-allowed and the spin-forbidden of 4f-5d transition, respectively. The experimental observation of the 4f-5d transition of Tb³⁺ is consistent well with the theoretical expectations.     

Lifetimes and oscillator strengths in the triplet system of ZnI

Selective laser excitation was used to measure the radiative lifetimes of the ZnI triplet states 4sns ³ S ₁(n=5–7) and 4snd ³ D ₃,³ D ₂ and³ D ₁(n=4–6). These states were excited from the metastable 4s4p ³ P states, which were collisionally populated in an atomic beam. The values are compared with the results of other experimental methods (beam-foil, pulsed electron excitation, Hanle effect) and with theoretical calculations. The corresponding oscillator strengths are discussed with respect to the astrophysical determination of the Zn photospheric abundance.     

Radiative decay and autoionization in the4 D-states of the 3d 94s5s configuration in CuI

The CuI 3d ⁹4s5s ⁴ D-states, which lie above the ionization limit, were populated by stepwise collisional and laser excitation. With respect to their total angular momentum, the⁴ D-states have completely different decay modes. Whereas the lifetimesτ(⁴ D _7/2)=8.2(4)·10^?9s andτ(⁴ D _1/2)=7.9(6)·10^?9 s are determinrd by radiative transitions and were measured by time-resolved spectroscopy, the lifetimesτ(⁴ D _5/2)=1.59(6)·10^?12s andτ(⁴ D _3/2)=1.28(5)·10^?12s are due to autoionization and were deduced from the widths of the excitation signals observed by ion detection.     

Hyperfine-structure investigation in the 6s5d configuration of135Ba and137Ba

The hyperfine structure of the metastable states of the 6s5d configuration of¹³⁵Ba and¹³⁷Ba has been studied by the atomic-beam magnetic resonance (ABMR) method. The metastable barium states were populated in a plasma-discharge inside the atomic-beam oven. The atoms emerging from the ABMR-apparatus were detected by the use of a dyelaser. Compared to conventional methods this technique has the advantage of being state selective. The following magnetic dipole and electric quadrupole interaction constantsa andb have been obtained:¹³⁷Ba:a(³ D ₁)=?520.536 (3) MHzb(³ D ₁)=17.890 (3) MHza(³D₂=415.928 (3) MHzb(³D₂)=25.899 (13) MHza(³D₃)=456.559 (4) MHzb ³D₃=47.390 (16) MHz¹³⁵Ba:a ³ D ₁=?465.166 (4) MHzb(³D₁)=11.642 (4) MHza(³D₂)=371.736(4) MHzb ³ D ₂=16.745 (14) MHza(³D₃)=408.038 (6) MHzb(³D₃)=30.801 (24) MHz Using these constants and the earlier known ones for the¹ D ₂ state the hyperfine structure for the 6s5d configuration has been analyzed with an effective hyperfine hamiltonian. Hyperfine parameters obtained from the analysis have been compared with theoretical values calculated with relativistic self-consistent-field (SCF) wavefunctions. The quadrupole moments have been evaluated with the following result Q(¹³⁵Ba) =0.20(3)b and Q(¹³⁷Ba) = 0.34(4)b uncorrected for the quadrupole shielding.     

Luminescence and crystal field analysis of Eu in Eu[Co(CN)6]·4H2O

The vibrational spectra of Eu[Co(CN)₆]·4H₂O and luminescence spectra of Eu³⁺ in this compound, using 355 nm excitation at temperatures down to 10 K, have been assigned. A clear distinction is made between the n=5 and 4 members of the Ln[M(CN)₆]·nH₂O series from the vibrational spectra. The electronic spectra show prominent vibronic structures, particularly for the ⁵D₀→⁷F₂ sideband. A resonance occurs between the transitions ⁵D₀→⁷F₁(III) and ⁵D₀→⁷F₀+ν(Eu−N). A crystal field analysis of the derived energy data set is presented for Eu³⁺ in eight coordination geometry.     

Facile synthesis and luminescence properties of uniform and monodisperse KY3F10:Ln3+ (Ln=Eu,Ce, Tb) nanospheres

Highly uniform and monodisperse KY₃F₁₀:Ln³⁺ (Ln=Eu, Ce, Tb) nanospheres, with an average diameter of 300 nm, have been successfully prepared through a simple template-free and surfactant-free stirring method under ambient conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize the samples. The SEM images illustrate that these spheres were actually composed of randomly aggregated nanoparticles. The doped rare earth ions show their characteristic emission in the KY₃F₁₀ samples, i.e., Eu^{3+ 5}D₀–⁷F_J (J=1, 2, 3, 4), Tb^{3+ 5}D₄–⁷F_J (J=6, 5, 4, 3, 2) and Ce³⁺ 5d–4f transition emissions, respectively. An energy transfer phenomenon from Ce³⁺ to Tb³⁺ has been observed in KY₃F₁₀ nanospheres, and the energy transfer efficiency depends on the doping concentration of Tb³⁺ if the concentration of Ce³⁺ is fixed.     

A reddish orange-emitting stoichiometric phosphor K3Eu(PO4)2 for white light-emitting diodes

A series of Eu³⁺ activated K₃Y_1?xEu_x(PO₄)₂ phosphors were synthesized by the solid-state reaction method. The structures and photoluminescent properties of these phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the monoclinic K₃Y(PO₄)₂ or K₃Eu(PO₄)₂. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370–410 nm) light. The orange emission from transition ⁵D₀–⁷F₁ is dominant, and the peak value ratio of ⁵D₀–⁷F₁/⁵D₀–⁷F₂ is 1.44. The emission spectra exhibit strong reddish orange performance (CIE chromaticity coordinates: x=0.63, y=0.36), which is due to the ⁵D₀–⁷F_J transitions of Eu³⁺ ions. The relationship between the structure and the photoluminescent properties of the phosphors was studied. The absence of concentration quenching of Eu³⁺ was observed in K₃Y_1?xEu_x(PO₄)₂. K₃Eu(PO₄)₂ has potential application as a phosphor for white light-emitting diodes.     

Study of the Rydberg nd D states of the thallium atom by the stepwise excitation method

The Rydberg nd ² D _{3/2, 5/2} states (n=15–30) of the thallium atom were studied by the method of two-stage excitation with subsequent ionization of the excited atoms by an electric field. The nd ² D levels were populated via the intermediate 7s ² S _1/2 states. The fine-structure splitting was found to be representable in the form of a combination of the terms depending on n*^?3 and n*^?5.     

Photoluminescence properties of Eu-doped ZnO films grown by sputtering-assisted metalorganic chemical vapor deposition

Photoluminescence (PL) properties of Eu-doped ZnO (ZnO:Eu) grown by a sputtering-assisted metalorganic chemical vapor deposition technique were investigated. In PL measurements at 300 K, the samples annealed at 600 °C for 30 min showed clear red-emission lines due to the intra-4f shell transition of ⁵D₀→⁷F_J (J=0–4) in Eu³⁺. In photoluminescence excitation (PLE) spectra, the PL was observed under the high-energy excitation above the band-gap energy of ZnO (indirect excitation) and the low-energy excitation resonant to the energy levels of ⁷F₀–⁵D₃ and ⁷F₀–⁵D₂ transitions in Eu³⁺ (direct excitation). The PL lifetime under the indirect excitation was shorter than that under the direct excitations. These PL properties revealed that the energy transfer from ZnO host to Eu³⁺ was accompanied under indirect excitation.     

Effect of modifier oxides on absorption and emission properties of Eu doped different lithium fluoroborate glass matrices

Eu³⁺ doped lithium fluoroborate glass with different modifier oxides (Li₂B₄O₇–BaF₂–NaF–MO where M=Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li₂B₄O₇–BaF₂–NaF–MgO+CaO, Li₂B₄O₇–BaF₂–NaF–CdO+PbO) were prepared by means of melt quenching method. These glass samples were analyzed by absorption, photoluminescence and decay curve measurements. The relative merits of thermal correction to the spectral intensities originating from the ground state (⁷F₀) of different absorption bands of Eu³⁺ are calculated. From the optical absorption measurements and using the Judd–Ofelt (J–O) theory, J–O parameters (Ω_λλ=2, 4 and 6) have been obtained which are used to predict the radiative properties such as radiative transition probabilities (A), radiative life-times (τ_R), and branching ratios (β_r) for certain transitions in all the glass matrices. From the emission spectra, peak stimulated emission cross-sections (σ_P) are obtained for the emission transitions, ⁵D₀→⁷F₁, ⁵D₀→⁷F₂, ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ of Eu³⁺ in lithium fluoroborate glass matrix with different modifier oxides. The fluorescence decay curves of the ⁵D₀→⁷F₂ transition have been measured and analyzed for all the glass matrices.     

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.     

Nuclear magnetic relaxation by self-diffusion in solid lithium:T 1-frequency dependence

We report on measurements of the⁷Li nuclear spin relaxation timeT ₁ in solid lithium as a function of temperature (?170°C≦T≦+180°C) and Larmor frequency (450kHz≦v _Li≦31.5 MHz). Using a relaxation model developed by Wolf and Cavelius and combining it with Seeger's diffusion formalism, the diffusion parameters for mono-and divacancy migration were evaluated by a least squares fit to the newly obtainedT ₁ data as well as to previousT _1? measurements. The result for the self-diffusion coefficientD ^SD is given byD ^SD=D ₁₀·exp(?Q ₁/RT)·[1+D ₂₁·exp(?Q ₂₁/RT)], withD ₁₀=0.038 cm²s^?1,Q ₁=12.0 kcal mol^?1,D ₂₁=250,Q ₂₁=4 kcal mol^?1 andR=1.98₅·10^?3 kcal mol^?1 degree^?1. Due to the flexibility of Seeger's formula, which contrasts with the standard Arrhenius interpretation of diffusion, discrepancies between earlier high- and low-frequency NMR investigations were eliminated. Furthermore, an excellent agreement with available results from tracer experiments was achieved by taking into account the theoretical predictions of the isotope effect and the vacancy correlation factor.     

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.