Enhanced luminescence of Tb by efficient energy transfer from Ce in Sr2B5O9Cl host

Ce³⁺ and Tb³⁺ co-doped Sr₂B₅O₉Cl phosphors with intense green emission were prepared by the conventional high-temperature solid-state reaction technique. A broad band centered at about 315 nm was found in phosphor Sr₂B₅O₉Cl: Ce³⁺, Tb³⁺ excitation spectrum, which was attributed to the 4f-5d transition of Ce³⁺. The typical sharp line emissions ranging from 450 to 650 nm were originated from the ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions. The photoluminescence (PL) intensity of green emission from Tb³⁺ was enhanced remarkably by co-doping Ce³⁺ in the Tb³⁺ solely doped Sr₂B₅O₉Cl phosphor because of the dipole-dipole mechanism resonant energy transfer from Ce³⁺ to Tb³⁺ ions. The energy transfer process was investigated in detail. In light of the energy transfer principles, the optimal composition of phosphor with the maximum green light output was established to be Sr_1.64Ce_0.08Tb_0.1Li_0.18B₅O₉Cl by the appropriate adjustment of dopant concentrations. The PL intensity of Tb³⁺ in the phosphor was enhanced about 40 times than that of the Tb³⁺ single doped phosphor under the excitation of their optimal excitation wavelengths.     

Enhanced luminescence of Ca3B2O6:Dy phosphors by Na-codoping for LED applications

The Ca_2.95−yDy_0.05B₂O₆:yNa⁺ (0≤y≤0.20) phosphors were synthesized at 1100 °C in air by the solid-state reaction route. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence excitation (PLE), photoluminescence (PL) spectra and thermoluminescence (TL) spectra. The PLE spectra show the excitation peaks from 300 to 400 nm due to the 4f-4f transitions of Dy³⁺. This mercury-free excitation is useful for solid-state lighting and light-emitting diodes (LEDs). The emission of Dy³⁺ ions on 350 nm excitation was observed at 480 nm (blue) due to the ⁴F_9/2→⁶H_15/2 transitions, 575 nm (yellow) due to ⁴F_9/2→⁶H_13/2 transitions and 660 nm (red) due to weak ⁴F_9/2→⁶H_11/2 emissions. The PL results from the investigated Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors show that Dy³⁺ emissions increase with the increase of the Na⁺ codoping ions. The integral intensity of yellow to blue (Y/B) can be tuned by controlling Na⁺ content. By the simulation of white light, the optimal CIE value (0.328, 0.334) can be achieved when the content of Na⁺-codoping ions is y=0.2. The results imply that the Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors could be potentially used as white LEDs.     

Enhanced white light emission in Er/Tm/Yb/Li codoped Y2O3 nanocrystals

Er/Tm/Yb codoped Y₂O₃ nanocrystals and Er/Tm/Yb/Li codoped Y₂O₃ nanocrystals have been synthesized by sol-gel method, bright white light emission has been observed at 976 nm excitation. The blue, green, and red emissions, respectively, arise from the transitions ¹G₄ → ³H₆ of Tm³⁺, ²H_11/2/⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_15/2 of Er³⁺ ion. Moreover, after doping Li⁺ ions into Er/Tm/Yb codoped Y₂O₃ nanocrystals, the white light emission increase greatly. CIE coordinate of Er/Tm/Yb/Li codoped Y₂O₃ nanocrystals is X = 0.32 and Y = 0.36 at 10 W/cm² excitation, which is very close to the standard equal energy white light illuminate (X = 0.33, Y = 0.33).     

The energy dependence of fusion in the 9Be+28Si system

The angular distributions of the energy spectra of the light charged particles (p, d and α) from the ⁹Be + ²⁸Si reaction have been measured in the energy range 12 ≦ E_lab ≦ 30 MeV. The particle evaporation spectra and the angular distributions were analyzed with a spin dependent statistical model. Angular distributions of ⁹Be ions elastically scattered on ²⁸Si have been measured at the energies 12 MeV, 17 MeV, 23 MeV and 30 MeV and were analysed, together with previously measured cross sections, with the optical model. The fusion cut-off angular momentum l_fus(E), the fusion cross section σ_fus(E) and the ratio σ_fus/σ_R^OM(E) were deduced. The excitation function for fusion was analyzed with the Glas and Mosel model. The parameters obtained from the fusion excitation function were compared with the corresponding ones from the ⁹Be + ²⁸Si optical-model interaction potential.     

Neutron-induced charged-particle reactions in 6Li and 9Be

Angular distributions of tritons from the ⁶Li(n, t)⁴He reaction were measured at E_n = 7.25, 6.77, 6.57, 5.24 and 4.71 MeV. Angular distributions of douterons from respectively, the ⁶Li(n, d)⁵He two-body breakup reaction were measured at E_n = 6.77 and 6.57 MeV, and of protons from the ⁶Li(n, p)⁶He reaction at E_n = 6.77, 5.24 and 4.71 MeV. All these reactions in ⁶Li were analyzed as direct interaction in the formalism of the distorted wave Born approximation. The optical model for the nuclear interaction was found to apply reasonably well to nuclei as light as ⁴He, ⁵He, ⁶He and ⁶Li. In addition, ⁶Li as an alpha-deuteron cluster gives the best bound-state wave function to describe the experimental angular distribution of tritons. The excitation functions at forward angles of the ⁶Li(n, t)⁴He, ⁶Li(n, d)⁵He and ⁶Li(n, p)⁶He reactions were measured for incident neutron energies between 4.4 and 7.3 MeV. It is found that the ⁶Li(n, d)⁵He two-body breakup reaction has a threshold at about E_n = 5.3 MeV. Angular distributions at E_n = 18.3 MeV for tritons and protons from the ⁹Be(n, t)⁷Li and ⁹Be(n, p)⁹Li, respectively, were also measured.     

The analyzing power Ay(θ) for the 9Be(p, n)9B reaction from 8 TO 15 MeV

The analyzing power A_y(θ) for the ⁹Be(p, n)⁹B reaction was measured at seven energies between 8.1 to 15.0 MeV for reaction angles between 0° and 100° (c.m.). The A_y(θ) values are predominantly negative and exhibit a smooth variation with energy. The significance of these results in Lane optical- model calculations for the ⁹Be + nucleon system and in comparisons between the observables P^y(θ) and A_y(θ) is indicated.     

Inelastic light scattering and photoluminescence in the mixed valence systems Eu3O4, Eu3S4 and Sm3S4

The thermally activated valence fluctuations of Eu₃S₄ and Sm₃S₄ have been studied using light scattering and photoluminescence techniques and are compared with measurements on the non-fluctuating compound Eu₃O₄, Eu₃S₄ exhibits an anomalous vibrational mode which is associated with the frequency factor of hopping, ν₂=1.3×10¹³ sec^?1. In Sm₃S₄ electronic Raman scattering is observed within the ⁷F₉ multiplet of the Sm²⁺ ion. An anomalous frequency shift of the5d-4f photoluminescence emission band in Eu₃S₄ is related to the temperature dependent fluctuation rate which passes through the reference time scale of the photoluminescence. Intra-4f photoluminescence has also been observed in Eu₃S₄ and Sm₃S₄.     

The ν5 and 2ν9 bands of the N isotopic species of nitric acid (H15NO3): Line positions and intensities

Nitric acid (HNO₃) plays an important role in the Earth’s atmosphere as a reservoir molecule of NO_x species. It has a strong infrared signature at 11 μm which is one of the most commonly used for the infrared retrieval of this species in the atmosphere since this spectral region coincides with an atmospheric window. It is therefore essential to have high quality spectral parameters in this spectral region. For the H¹⁴NO₃ (main) isotopic species, the 11 μm bands were already the subject of numerous extensive studies which involve not only the ν₅ and 2ν₉ cold bands but also the first hot bands. The present work is the first high resolution Fourier transform analysis of the 11 μm bands for H¹⁵NO₃, which is the second most abundant isotopomer of nitric acid [a ≅ 0.00365(7)]. In this way, the analysis of the ν₅ and 2ν₉ cold bands centered at 871.0955 and 893.4518 cm⁻¹ was performed, and as for H¹⁴NO₃, these bands are significantly perturbed since rather strong resonances couple the 5¹ and 9² rotational levels. The theoretical model that we used to compute the line positions and line intensities is directly issued from the one which we used recently for H¹⁴NO₃ [A. Perrin, J. Orphal, J.-M. Flaud, S. Klee, G. Mellau, H. Mäder, D. Walbrodt, M. Winnewisser, J. Mol. Spectrosc. 228 (2004) 375-391]. Actually, for the H¹⁵NO₃ line positions, the Hamiltonian matrix accounts for the rather strong Fermi and the weaker Coriolis interactions linking the 5¹⇔9² rotational levels. Using this model which accounts correctly for the strong mixing of the 5¹ and 9² upper state energy levels, the ν₅ and 2ν₉ line intensities for H¹⁵NO₃ were satisfactorily computed using the ν₅ and 2ν₉ transition moment operators achieved previously for the ¹⁴N (main) isotopic species. In this way, the transfer of intensities from the ν₅ fundamental (and presumably strong) band to the 2ν₉ overtone (and presumably weak) band could be explained for H¹⁵NO₃ as it was done previously for the ¹⁴N (main) isotopic species. Finally, the position of the H¹⁵NO₃ν₅ + ν₉ − ν₉ hot band was identified at 875.245 cm⁻¹.     

High-resolution infrared study of Coriolis resonances in the ν9 and ν10 bands of allene-d4

The infrared perpendicular bands ν₉ and ν₁₀ in allene-d₄, which are located at 824 and 666 cm^?1, respectively, have been studied at a resolution near to 0.010 cm^?1. The bands were analyzed by taking into account the z-Coriolis resonance between these bands and the (x,y)-Coriolis resonance between ν₁₀ and ν₄(B₁), which is only Raman active. Upper-state parameters and interaction constants are derived from this analysis. Additional Coriolis interactions between ν₉ and ν₃(A₁) as well as between ν₁₀ and 2ν₁₁²(B₁,B₂) are also discussed. Special attention is paid to the study of l-type doublings. Doublets due to q^(?) doubling were resolved both in ν₉ and in ν₁₀. l-type doubling constants including their signs are also obtained.     

The high-resolution infrared spectrum of ethane-1,1,1-D3 rovibration analyses of the pseudoperpendicular A1A2ν9 + ν10 band and the parallel ν3 + ν4 and ν5 bands

A complete vibration-rotation analysis was made of the A₁A₂ combination band ν₉ + ν₁₀ of CH₃CD₃ at 2582 cm^?1. This band exhibits pseudoperpendicular structure due to the large effective Coriolis interaction constant (ζ ≈ 0.7), which couples the almost degenerate A₁ and A₂ vibrational components for all nonzero values of the rotational quantum number K, and gives a subband Q-branch spacing of 2.5 cm^?1. The location of the band center is assisted through an interruption of the perpendicular-like structure, since both K = 0 Q branches are forbidden by the vibrational and rotational selection rules. The conventional A₁ parallel bands ν₃ + ν₄ at 2507 cm^?1 and ν₅ (CC stretch) at 905 cm^?1 were also analyzed. For ν₅, a combination of numerical analysis and band contour simulation was used to determine a set of upper-state rotation parameters. Combination of the present results with previous data for ν₉ and 2ν₃ permits rotational parameters to be derived for the ν₄ and ν₁₀ fundamentals of CH₃CD₃. Neither of these fundamentals are amenable to straightforward analysis, both being very weak in the infrared and overlaid by the intense ν₁₁ fundamental.     

Analysis of the ν9 and ν10 bands of cyclopropane

The infrared spectrum of gaseous cyclopropane has been measured in the regions 980–1080 and 1400–1500 cm^?1, containing the ν₁₀ and ν₉E′ fundamental bands, respectively, using a high-resolution Fourier transform instrument. Deconvolution was used to enhance the resolution in the crowded parts of the spectrum to ～0.0020–0.0025 cm^?1. Apart from the rotational l-resonance affecting mainly the low-K subbands, the ν₉ band is strongly perturbed by Fermi resonance with the 2ν₁₄² state lying ～41 cm^?1 above. The effects of the Fermi resonance are most pronounced in the high-KΔK = +1 subbands as the 2ν₁₄^?2 levels would cross the ν₉⁺ levels near K = 30. ^rR lines of 2ν₁₄^?2 for K = 24 to 36, enhanced by the resonance, have been identified in the region 1469–1475 cm^?1 of the spectrum. Two extra perturbation-enhanced subbands are found adjacent to the K = 16?17 and K = 17?16 subbands of ν₉: these have been ascribed to the K = 18?17 transitions in 2ν₁₄^?2 and to the K = 19?16 transitions in $\text{ν}{}_2\text{2ν}{}_{14}{}^0$, respectively, as their upper states coincide with the corresponding levels ν₉^?(K = 16) and ν₉⁺(K = 17). A combination of l-resonance and Fermi resonance is mainly responsible for the interactions causing the perturbations and appearance of the extra subbands, but a direct rotational interaction 〈ν₉^?(K)|h₃|2ν₁₄^?2(K + 2)〉 also had to be introduced to accurately account for the observations. In contrast, the ν₁₀ band is not appreciably perturbed by other states and merely exhibits effects of strong l-resonance in the low-K subbands, and K-doubling of the high-J lines of the K = 2–3 subband. A detailed analysis of the spectrum and of the perturbations is described and sets of accurate spectroscopic constants are reported for ν₁₀ and ν₉ as well as for the perturbing state 2ν₁₄², which reproduce 3020 observed lines of the ν₁₀ band with a standard deviation of 0.0008 cm^?1 and 1810 lines of ν₉ with a standard deviation of 0.0010 cm^?1.     

Diode laser measurements of the band strengths of ν3 and ν6 in 12CH3D

A diode laser spectrometer has been used to measure line strengths for 143 transitions in the ν₆ fundamental band of ¹²CH₃D near 9 μm. These line-strength measurements have been used to derive a band strength for ν₆ and ν₃. The band strength derived for ν₆ is 61.7 ± 1.8 cm^?2 atm^?1, and that for ν₃ is 49.3 ± 1.4 cm^?2 atm^?1 at 395 K.     

Photocontrol of magnetization in Al-substituted Fe3O4 thin films

Thin films of (111)-oriented spinel ferrite Al_0.5Fe_2.5O₄ have been prepared by a pulsed-laser deposition (PLD) technique on α-Al₂O₃ (0001) substrates. The films exhibit cluster-glass behaviors with a spin-freezing temperature, T_g, near or above room temperature. The magnetization was found to increase following light irradiation below T_g, which indicates the photoinduced melting of cluster-glass states. An analysis comparing the dynamic behavior of magnetic response to light irradiation between zero-field-cooled (ZFC) states and field-cooled (FC) states at 10 K under various light intensities, I, revealed that the direct photoexcitation of spins occurs when I≤0.78 mW/mm², while the thermal heating effect following the light absorption of the samples also contributes to the enhancement of magnetization when I≥1.22 mW/mm². The magnetization of the films could be controlled by light irradiation even at room temperature. This suggests the possibility of utilizing these films in the development of novel magneto-optical memory devices.     

Hyperfine characterization of Bi1.9Te0.1SrNb1.9Hf0.1O9

The Aurivillius type oxide Bi_1.9Te_0.1SrNb_1.9Hf_0.1O₉ has been studied by Perturbed Angular Correlations spectroscopy using ¹⁸¹Ta probes. The spin precession curves were measured from room temperature up to 873 K. Two sites are occupied by probes and the temperature dependence of both indicates a continuous phase transition at about 625 K. One site is ordered while the other is disordered. This situation is analyzed in terms of simple models already applied to perovskites. The transition temperature of the solid solution Bi_2−xTe_xSrNb_2−xHf_xO₉ (with 0≤x≤0.5) shows a strong dependence on composition.     

Preparation and luminescent properties of BaCa2Si3O9:Eu

A blue emitting phosphor of the triclinic BaCa₂Si₃O₉:Eu²⁺ was prepared by the combustion-assisted synthesis method and an efficient blue emission ranging from the ultraviolet to visible was observed. The luminescence and crystallinity were investigated using luminescence spectrometry and X-ray diffractometry (XRD), respectively. The emission spectrum shows a single intensive band centered at 445 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The excitation spectrum is a broad extending from 260 to 450 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu²⁺ in BaCa₂Si₃O₉:Eu²⁺ phosphor is about 0.05 mol. The corresponding concentration quenching mechanism is verified to be a dipole-dipole interaction. The CIE of the optimized sample Ba_0.95Ca₂Si₃O₉:Eu_0.05²⁺ was (x, y)=(0.164, 0.111). The result indicates that BaCa₂Si₃O₉:Eu²⁺ can be potentially useful as a UV radiation-converting phosphor for white light-emitting diodes (LEDs).     

Light induced charge transfer processes in Cr doped Bi12GeO20 and Bi12SiO20 single crystals

Optical absorption and ESR spectra of Bi₁₂GeO₂₀ doped with Cr were measured before and after illumination with visible light. It was found that Cr⁴⁺ ions in tetrahedral position are responsible for light induced ESR and optical spectra. The g-factor of the center is 1.945 ± 0.002. Crystal field parameters for the Cr⁴⁺ center are D_q = 820 cm^?1 and B = 429cm^?1. The photochromic effect is explained in terms of a Cr⁵⁺?Cr⁴⁺ charge transfer process.     

Relaxation of the 4G92 state of Nd3+ in LaCl3 and Nd3+ in La(Cl99.6Br0.4)3

The decay of the ⁴G_{$\text{9}\text{2}$} state of Nd³⁺ in LaCl₃ and La(Cl_99.6 Br_0.4)₃ was measured after pulsed laser excitation as a function of temperature. The decay rate is shown to depend besides the radiative transition on single-phonon relaxation between the states ⁴G_{$\text{9}\text{2}$} ($\text{μ =}\text{1}\text{2}$) and ⁴G_{$\text{9}\text{2}$} ($\text{μ =}\text{3}\text{2}$) and on multiphonon orbit-lattice relaxation from ⁴G_{$\text{9}\text{2}$} to ²G_{$\text{9}\text{2}$}. Partial substitution of Cl by Br only alters the radiative lifetime.     

ν7 and ν9 bands of formic acid near 16 μm

The ν₇ and ν₉ fundamental bands of formic acid were studied by Fourier transform spectroscopy with a resolving power of 0.020 cm^?1. Band centers obtained are ν₇ = 626.158 cm^?1 and ν₉ = 640.722 cm^?1. It was possible to determine rotational and centrifugal distortion parameters for both vibrational states v₇ = 1 and v₉ = 1 and also the two first-order Coriolis interaction parameters along z and x axes and the second-order Coriolis parameter along z axis. The stability of rotational and distortion parameters compared to ground state values confirms that a Watson type Hamiltonian is well adapted to such a problem.     

Emission and excitation spectra of Bi2Ge3O9:Eu3+

The emission and excitation spectra of the Bi₂Ge₃O₉:Eu crystal are observed at 77 K and 297 K. The spectra contain groups of sharp lines which are attributed to the transitions within 4f⁶ (Eu³⁺) configuration. The numbers of Stark splitting of terminal levels of transitions from ⁵D₀ and ⁷F₀ multiplets indicate that Eu³⁺ substitutes for Bi³⁺ in Bi₂Ge₃O₉. Tentative assignment of Stark levels of ⁷F_0-4 multiplets is made to crystal quantum numbers of C₃ symmetry which represents the site symmetry of Bi³⁺ in Bi₂Ge₃O₉. The following set of values of crystal field parameters of the C₃ point group is found to give the best overall agreement between the observed energy levels and the calculated levels: B²₀ = -533.84 cm^-1, B⁴₀ = 1085.99 cm^-1, Re(B⁴₃) = 327.57 cm^-1, Im(B⁴₃) = 75.209 cm^-1, B⁶₀ = 185.02 cm^-1, Re(B⁶₃) = - 68.475 cm^-1, Im(B⁶₃) = - 300.45 cm^-1, Re(B⁶₆) = 137.24 cm^-1 and Im(B⁶₆) = 882.29 cm^-1.     

The ν2 and ν4 bands of AsH3

The infrared absorption of arsine, AsH₃, between 750 and 1200 cm^?1 has been recorded at a resolution of 0.006 cm^?1. Altogether 2419 transitions, including nearly 700 “perturbation allowed” transitions with Δ∥k ? l∥ = ±3, ±6, and ±9, have been assigned to the ν₂(A₁) and ν₄(E) bands. Splitting of the transitions for K″ = 3, 6, and 9 was also observed. To fit the rotational pattern of the v₂ = 1 and v₄ = 1 vibrational states up to J = 21, all the experimental data were analyzed simultaneously on the basis of a rovibrational Hamiltonian which took into account the Coriolis interaction between ν₂ and ν₄ and also included several essential resonances within them. The derived set of 38 significant spectroscopic parameters reproduced the 2328 transition wavenumbers retained in the final fit within the accuracy of the experimental measurements.