Luminescence properties of Dy3+ or/and Sm3+ doped LiLa(WO4)2 phosphors and energy transfer from Dy3+ to Sm3+

The Dy³⁺ or/and Sm³⁺ doped LiLa(WO₄)₂ phosphors are synthesized by a facile solid state reaction method. The phase and luminescence properties of the phosphors are investigated. The powder X-ray diffraction (XRD) results show that the phosphor has a tetragonal phase crystal structure. The quenching concentration of single doped Dy³⁺ and Sm³⁺ in the LiLa(WO₄)₂ are determined to be 6% and 3%, respectively. Under the excitation of 404 nm, warm white light is obtained in the co-doped phosphors. With the concentration of Sm³⁺ increasing, the correlated color temperature (CCT) gradually decreases from 3090 to 2453 K. Two kinds of energy transfer may exist at the same time. The overlap between the emission spectrum of Dy³⁺ and the excitation spectrum of Sm³⁺ reveals that the energy of Dy³⁺ can transfer to Sm³⁺ via radiation. Another way of energy transfer, that is non-radiative energy transfer, is attributed to the excited state of Dy³⁺ (⁴F_9/2) slightly higher than that of Sm³⁺ (⁴I_19/2). The calculation results show that non-radiative energy transfer process from Dy³⁺ to Sm³⁺ ions is predominated by quadrupole–quadrupole interaction.     

An ab initio molecular orbital study of the trimethylgallium-arsine adduct: (CH3)3Ga:AsH3

The structure, harmonic frequencies, and binding energy of the trimethylgallium-arsine adduct, (CH₃)₃Ga: AsH₃, have been computed using ab initio molecular orbital methods, and, where possible, compared with experimental results. The structures and frequencies of the precursors trimethylgallium and arsine are perturbed to only a small extent upon adduct formation. The binding energy of (CH₃)₃Ga: AsH₃ is found to be 5.2 kcal/mol lower than that for H₃Ga:AsH₃ at the MP2/HUZSP^*//RHF/HUZSP^* level of computation.     

Effect of External Pressure on the Excitation Energy Transfer from [Cr(ox)3]3− to [Cr(bpy)3]3+ in [Rh1−xCrx(bpy)3][NaM1−yCry(ox)3]ClO4

Resonant excitation energy transfer from [Cr(ox)₃]^3? to [Cr(bpy)₃]³⁺ in the doped 3D oxalate networks [Rh_1?xCr_x(bpy)₃][NaM^III_1?yCr_y(ox)₃]ClO₄ (ox=C₂O₄^?, bpy=2,2′‐bipyridine, M=Al, Rh) is due to two types of interaction, namely super exchange coupling and electric dipole–dipole interaction. The energy transfer probability for both mechanisms is proportional to the spectral overlap of the ²E→⁴A₂ emission of the [Cr(ox)₃]^3? donor and the ⁴A₂→²T₁ absorption of the [Cr(bpy)₃]³⁺ acceptor. The spin‐flip transitions of (pseudo‐)octahedral Cr³⁺ are known to shift to lower energy with increasing pressure. Because the shift rates of the two transitions in question differ, the spectral overlap between the donor emission and the acceptor absorption is a function of applied pressure. For [Rh_1?xCr_x(bpy)₃][NaM_1?yCr_y(ox)₃]ClO₄ the spectral overlap is thus substantially reduced on increasing pressure from 0 to 2.5 GPa. As a result, the energy transfer probability decreases with increasing pressure as evidenced by a decrease in the relative emission intensity from the [Cr(bpy)₃]³⁺ acceptor.     

Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G^*//HF/6-31G^*+ZPE(HF/6-31G^*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe₃F₃ ⁺ cation detected in the mass spectra of μ₄-Be₄O(CF₃COO)₆ were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol⁻¹ and those of the remaining four structures lie in the range 20–40 kcal mol⁻¹. Two most favorable isomers, aC _2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC _3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol⁻¹, except for the pyramidalC _3v isomer (∼16 kcal mol⁻¹). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol⁻¹). A planarD _3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe₃H₃ ⁺ cation, a hydride analog of the OBe₃F₃ ⁺ ion; the energies of the remaining five isomers are more than 25 kcal mol⁻¹ higher. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999.     

Energetics of the loss of H2 from [C3H7]+

The internal energies of [C₃H₇]⁺ ions contributing to the metastable peak [C₃H₇]⁺ → [C₃H₅]⁺ + H₂ are higher (by perhaps > 100 kJ mol^?1) than those of the ion contributing to the threshold current in appearance energy measurements on [C₃H₅]⁺. The measured appearance energy may lead to an underestimation of the activation energy, i.e. negative ‘kinetic shift’, due to quantum, mechanical tunnelling. The distribution of energy released in the decomposition can be explained on the basis that much of the reverse activation energy and a statistical proportion of the excess energy is released as translation.     

Research on Molecular Structure and Electronic Properties of Ln3+ (Ce3+, Tb3+, Pr3+)/Li+ and Eu2+ Co-Doped Sr2Si5N8 via DFT Calculation

We use density functional theory (DFT) to study the molecular structure and electronic band structure of Sr₂Si₅N₈:Eu²⁺ doped with trivalent lanthanides (Ln³⁺ = Ce³⁺, Tb³⁺, Pr³⁺). Li⁺ was used as a charge compensator for the charge imbalance caused by the partial replacement of Sr²⁺ by Ln³⁺. The doping of Ln lanthanide atom causes the structure of Sr₂Si₅N₈ lattice to shrink due to the smaller atomic radius of Ln³⁺ and Li⁺ compared to Sr²⁺. The doped structure’s formation energy indicates that the formation energy of Li⁺, which is used to compensate for the charge imbalance, is the lowest when the Sr2 site is doped. Thus, a suitable Li⁺ doping site for double-doped lanthanide ions can be provided. In Sr₂Si₅N₈:Eu²⁺, the doped Ce³⁺ can occupy partly the site of Sr₁²⁺ ([SrN₈]), while Eu²⁺ accounts for Sr₁²⁺ and Sr₂²⁺ ([SrN₁₀]). When the Pr³⁺ ion is selected as the dopant in Sr₂Si₅N₈:Eu²⁺, Pr³⁺ and Eu²⁺ would replace Sr₂²⁺ simultaneously. In this theoretical model, the replacement of Sr²⁺ by Tb³⁺ cannot exist reasonably. For the electronic structure, the energy level of Sr₂Si₅N₈:Eu²⁺/Li⁺ doped with Ce³⁺ and Pr³⁺ appears at the bottom of the conduction band or in the forbidden band, which reduces the energy bandgap of Sr₂Si₅N₈. We use DFT+U to adjust the lanthanide ion 4f energy level. The adjusted 4f-CBM of Ce_Sr1Li_Sr1-Sr₂Si₅N₈ is from 2.42 to 2.85 eV. The energy range of 4f-CBM in Pr_Sr1Li_Sr1-Sr₂Si₅N₈ is 2.75–2.99 eV and its peak is 2.90 eV; the addition of Ce³⁺ in Eu_Sr1Ce_Sr1Li_Sr1 made the 4f energy level of Eu²⁺ blue shift. The addition of Pr³⁺ in Eu_Sr2Pr_Sr2Li_Sr1 makes part of the Eu²⁺ 4f energy level blue shift. Eu²⁺ 4f energy level in Eu_Sr2Ce_Sr1Li_Sr1 is not in the forbidden band, so Eu²⁺ is not used as the emission center.     

颜色可调Sr3Y（BO3）3∶Tm3+，Dy3+荧光粉的发光性能及能量传递

采用高温固相法制备了Sr_3Y(BO_3)_3:xTm~(3+),yDy~(3+)荧光粉,并通过XRD、SEM和荧光光谱仪对样品的物相、微观形貌、发光性能、能量传递机制和CIE色坐标进行了分析。结果表明:Sr_3Y(BO_3)_3:xTm~(3+)荧光粉在监测波长为359 nm时发射蓝光,Tm~(3+)的浓度淬灭点为x=0.08;在Sr_3Y(BO_3)_3:0.08Tm~(3+),yDy~(3+)荧光粉中,随着Dy~(3+)掺杂浓度的增加,Tm~(3+)的发光强度降低而Dy~(3+)发光强度却先增加后降低,Dy~(3+)的浓度淬灭点为y=0.1;通过改变Dy~(3+)掺杂浓度或改变激发光的波长,均可实现发射光的颜色可调;在Tm~(3+)-Dy~(3+)离子之间存在能量传递。当Dy~(3+)掺杂浓度(物质的量分数)为0.15时能量传递效率达75.14%,能量传递机制为电偶极-电偶极相互作用。     

Energy transfer between Bi3+ and Nd3+ in germanate glass

Energy transfer from Bi³⁺ to Nd³⁺ is reported in germanate glass. It was found that the excitation range and intensities of the ⁴F_{$\text{3}\text{2}$} → ⁴I_{$\text{9}\text{2}$}, ⁴I_{$\text{11}\text{2}$} emissions are increased several fold when excited through ¹S₀ → ³P₁ absorption of Bi³⁺. It is shown that the energy transfer is nonradiative. The energy transfer probability and efficiency were calculated from the Bi³⁺ fluorescence decay rates and intensities. The Bi³⁺ → Nd³⁺ energy transfer may be utilized in Nd³⁺ glass laser.     

Eu3+ concentration dependent optical properties and energy transfer from host Gd3+ to Eu3+ in GdF3 nanocrystals

By using a hydrothermal method, a series of Eu³⁺ concentration dependent GdF₃ nanocrystals have been synthesized. The crystalline structures of samples are characterized by XRD patterns, the morphology and size of the samples are illustrated by FE-SEM images, and the optical properties of the samples are presented by PL excitation and emission spectra. The energy transfer from host Gd³⁺ to Eu³⁺ is observed in the Eu³⁺ doped GdF₃ nanocrystals. The optical properties of Eu³⁺ and the energy transfer efficiency from host Gd³⁺ to Eu³⁺ are discussed on the basis of the Eu³⁺ concentration dependent integrated PL excitation and emission spectra of Gd³⁺ and Eu³⁺. The discussion on optical properties of Eu³⁺ and the energy transfer from Gd³⁺ to Eu³⁺ is meaningful to design and synthesize Gd³⁺ based compounds.     

On the existence of SH3, SeH3, and TeH3: Discrepancies between all-electron and pseudopotential calculations

Ab initio calculations using both pseudopotential and double and triple-ζ all-electron basis sets, with and without electron correlation (MP2, QCISD), have been performed on the λ⁴-sulfanyl (SH₃), λ⁴-selanyl (SeH₃), and λ⁴-tellanyl (TeH₃) radicals. All-electron basis sets of double-ζ quality predict that SH₃ and SeH₃ correspond to transition states on their respective potential energy surfaces. In contrast, the pseudopotentials of Hay and Wadt predict that SH₃ and SeH₃ correspond to local minima at the QCISD level of theory while the pseudopotentials of Christiansen and Stevens predict transition states. By comparison, TeH₃ proved to be a local minimum at all levels of theory. Interestingly, when a very large (triple-ζ) all-electron basis set was used, SH₃ proved to be a transition state; however, in this instance the potential energy surface was found to be much flatter than in the case for which a double-ζ basis set was used, suggesting that further improvements in the basis set may lead to a local minimum. Further improvements in the all-electron selenium basis also led to a local minimum for SeH₃ at the QCISD level of theory. © 1995 by John Wiley & Sons, Inc.     

Energetics of proton transfer between carbon atoms (H3CH ? CH3)−

Ab initio calculations were carried out to study the potential energy surface of (H₃C? H? CH₃)^?. The 6–31G* basis set is supplemented by a set of diffuse p functions on both C and H (with a range of exponents for the latter). The binding energy of CH₄ and CH₃^? to form the (H₃CH? CH₃)^? complex is about 2 kcal/mol, much smaller than for comparable ionic H-bonded systems involving O or N atoms. Nearly half of this interaction energy is due to correlation effects, computed at second and third orders of Møller-Plesset perturbation theory. Correlation is also responsible for substantial reductions in the energy barrier to proton transfer within the complex. This barrier is computed to be 13?15 kcal/mol at the MP3 level, depending upon the exponent used for the H p functions.     

Energy migration in one-dimensional Li6Eu(BO3)3

Analysis of the luminescence properties of Eu³⁺ in Li₆Eu(BO₃)₃ suggests that the energy migration which occurs over the Eu³⁺ sublattice down to low temperatures is one-dimensional. The temperature dependence of the migration points to a two-site non-resonant two-phonon assisted process. It occurs by exchange interaction.     

A novel Sr3Y(PO4)3-based white light-emitting phosphor

The Sr₃Y(PO₄)₃:0.05Sm³⁺, Sr₃Y(PO₄)₃:0.005Tb³⁺, and Sr₃Y(PO₄)₃:0.005Tb³⁺, 0.05Sm³⁺ phosphors were synthesized using a conventional solid-state reaction technique at high temperature and their photoluminescence properties under ultraviolet (UV) excitation were studied. We observed the UV sensitization of Sm³⁺ emission (565, 600, and 648 nm) by Tb³⁺ in Sr₃Y(PO₄)₃:0.005Tb³⁺, 0.05Sm³⁺, that leads to a white light emission with the CIE coordinate (0.367, 0.312) of Sr₃Y(PO₄)₃:0.005Tb³⁺, 0.05Sm³⁺ phosphor under UV excitation. The emission is a result of partial energy transfer from Tb³⁺ to Sm³⁺, which is discussed in detail in terms of the corresponding excitation and emission spectra.     

M5(PO4)3F (M=Ca, Sr, Ba)中Sm3+的电荷迁移态及Sm3+和Eu3+的电荷迁移能量关系

采用高温固相反应合成了M_5-2xSm_xNa_x(PO₄)₃F(M=Ca,Sr,Ba)荧光体,研究了其在真空紫外-可见光范围的发光特性。发现在Ca₅(PO₄)₃F中Sm³⁺的电荷迁移带约在191 nm,在Sr₅(PO₄)₃F中约在199 nm,而在Ba₅(PO₄)₃F中约在204 nm,随着被取代碱土离子半径的增大电荷迁移能量逐渐减小。比较了M₅(PO₄)₃F (M=Ca,Sr,Ba)中Sm³⁺和Eu³⁺电荷迁移能量的关系。     

Enhanced Supercapacitor Performance Using a Co3O4@Co3S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co₃O₄ and Co₃S₄ on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co₃O₄@Co₃S₄ nanocomposite, the nanostructure of Co₃S₄ was fabricated from Co₃O₄ nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm⁻² (5651.24 F g⁻¹) at a current density of 6 mA cm⁻² compared to the Co₃O₄/rGO/NF electrode with a capacitance of 3.06 F cm⁻² (1230.77 F g⁻¹) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg⁻¹, specific power density of 6048.03 W kg⁻¹ and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s⁻¹). Finally, by using Co₃O₄ @Co₃S₄/rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm⁻² at the applied current density of 1 mA cm⁻², and delivered an energy density of 0.143 Wh kg⁻¹ at the power density of 5.42 W kg⁻¹.     

Photofragmentation of CF3I in the A band

CF₃I is photodissociated in a molecular beam with 248 nm laser lighl. Fragmentation takes place into CF₃ and I(²P_3/2) or I(²P_1/2). The quantum yield for excited I (I* = I(²P_1/2)) formation is determined to be 0.92. The CF₃ fragments are found to be considerably vibrationally excited. Of the available energy in the CF₃ + I* channel 39% (0.69 eV) appears on the average as vibrational energy in the CF₃ radical. The angular distributions in both channels show predominantly parallel character. It can be concluded that at this wavelength 97% of the total absorption is due to the ³Q₀ ← ¹A₁ transition and only 3% to the ¹Q ← ¹A₁ transition. Most of the signal in the CF₃ + I channel originates from an effective crossing between the ³Q₀ and ¹Q states. A coupled channel calculation is performed to obtain a better insight into the dissociation dynamics of the CF₃I molecule. The results indicate that the CF₃ fragments from dissociation of CF₃I at 248 nm may be expected to be vibrationally excited. However, the experimental distribution has a higher average energy and is much broader. An explanation for this phenomenon is suggested.     

Effcient Near-Infrared Quantum Cutting in Tm3+/Yb3 Codoped LiYF4 Single Crystals for Solar Photovoltaic

Downconversion (DC) with emission of two near-infrared photons about 1000 nm for each blue photon absorbed was obtained in thulium (Tm³⁺) and ytterbium (Yb³ ) codoped yt-trium lithium fluoride (LiYF₄) single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were measured through photoluminescence excitation, emission spectra and decay curves. Luminescence between 960 and 1050 nm from Yb³ : ²F_5/2→²F_7/2 transition, which was originated from the DC from Tm³ ions to Yb³ ions, was observed under the excitation of blue photon at 465 nm. Moreover, the energy transfer processes were studied based on the Inokuti-Hirayama model, and the results indicated that the energy transfer from Tm³ to Yb³ was an electric dipole-dipole interaction. The max-imum quantum cutting effciency approached up to 167.5% in LiYF₄ single crystal codoped with 0.49mol% Tm³ and 5.99mol% Yb³ . Application of this crystal has prospects for increasing the energy e ciency of crystalline Si solar cells by photon doubling of the high energy part of the solar spectrum     

Diffusion-limited energy transfer from Dy3+ to Ho3+ in dimethyl sulfoxide

Diffusion-limited energy transfer has been studied from Dy³⁺ to Ho³⁺ in dimethyl sulfoxide. The value of the diffusion constant has been calculated to be 4.65 × 10⁻¹⁴ cm² sec⁻¹ at 300 K. A temperature-dependent study of energy transfer has also been carried out. The probabilities of energy transferP_da and transfer efficiencyη_T have been calculated.     

Dynamics of the CH3 + OH reaction

We study dynamics of the CH₃ + OH reaction over the temperature range of 300–2500 K using a quasiclassical method for the potential energy composed of explicit forms of short‐range and long‐range interactions. The explicit potential energy used in the study gives minimum energy paths on potential energy surfaces showing barrier heights, channel energies, and van der Waals well, which are consistent with ab initio calculations. Approximately, 20% of CH₃ + OH collisions undergo OH dissociation in a direct‐mode mechanism on a subpicosecond scale (<50 fs) with the rate coefficient as high as ～10^?10 cm³ molecule^?1 s^?1. Less than 10% leads to the formation of excited intermediates CH₃OH? with excess vibrational energies in CO and OH bonds. CH₃OH? stabilizes to CH₃OH, redissociates back to reactants, or forms one of various products after intramolecular energy redistribution via bond dissociation and formation on the time scale of 50–200 fs. The principal product is ¹CH₂ (k being ～10^?11), whereas ks for CH₂OH, CH₂O, and CH₃O are ～10^?12. The minor products are HCOH and CH₄ (k～10^?13). The total rate coefficient for CH₃ + OH → CH₃OH? → products is ～10^?11 and is weakly dependent on temperature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 455–466, 2011     

Conformational analysis of X3PNP(O)X2 and (X3PNPX3)+ for X = H,F, Cl,CH3 by the pcilo method

Conformational energy maps have been calculated, using the PCILO method, for X₃PNP(O)X₂ and (X₃PNPX₃)⁺ for X = H, F, Cl, CH₃ as a function of the PNP angle. In H₃PNP(O)H₂ the global energy minimum corresponds to the eclipsed conformation of the H₃P and P(O)H₂ fragments for all PNP angles, while in Cl₃PNP(O)Cl₂, the global minimum always has Cl₃P and P(O)C1₂ staggered: the global minimum in F₃PNP(O)F₂ corresponds to eclipsed F₃P and P(O)F₂ fragments at low PNP angles and staggered fragments at high PNP angles: in (CH₃))₃PNPO(CH₃)₂ the global minimum conformation is very sensitive to ∠ PNP. Subordinate energy minima occur for all X₃PNP(O)X₂, species: in particular, there are two local conformational minima for Cl₃PNP(O)Cl₂ at the optimum value of ∠ PNP, and the relative energies of the three stable conformations are in good agreement with those derivable from the ³¹P NMR spectrum of this compound. In (X₃PNPX₃)⁺ the global minimum, usually the sole minimum on the conformational energy surface, is always close to the eclipsed conformation: free rotation of the X₃P groups relative to one another is approached in each (X₃PNPX₃)⁺ ion as ∠PNP approaches 180°. The conformations of the transition states for the equilibria between energy minima are reported with their relative energies, for X₃PNP(O)X₂ (X = H, F. Cl, CH₃) and for (Cl₃PNPCl₃)⁺