Investigation of emission spectra and lifetimes of Cs2NaErCl6 single crystals

The fluorescence spectra and lifetimes of low lying states of Er³⁺ in Cs₂NaErCl₆ single crystals have been investigated at room temperature and at 77 K. The assignments of the ⁴F_{$\text{9}\text{2}$}-⁴I_{$\text{15}\text{2}$} and ⁴I_{$\text{11}\text{2}$}-⁴I_{$\text{15}\text{2}$} phonon-assisted transitions have been proposed. The fluorescence lifetimes of low lying fluorescing levels have been estimated.     

Laser time-resolved selective excitation of Nd3+ ions in KNdP4O12 crystals

The emission spectra of Nd³⁺ ions in KNd_xRE_1?xP₄O₁₂ (RE = Y, La and Pr) and KNd_xCr_1?xP₄O₁₂ crystals were investigated. Under selective excitation into ²G$\text{7}\text{2}$ + ⁴G$\text{5}\text{2}$ multiples at 1.6 K the fluorescence of Nd³⁺ ions in non-equivalent crystal sites was observed. The excitation spectrum of the ${}^4\text{F}\text{3}\text{2}$ fluorescence had a complex satellite structure. Time resolved measurements showed the dependence of the fluorescence decay on the excitation wavelength. Selective excitation into the satellite lines at the wings of the main transition led to strongly non-exponential decay. The low temperature results indicated that there is no spectral energy transfer between ions in different types of sites.     

Spectral and temperature characteristics of Cs2Na(Er,Yb, Y)Cl6 upconverters

Spectral luminescence characteristics of the Cs₂Na(Er, Yb, Y)Cl₆ type upconverter have been measured in the range 300–650 K. A nearly sixfold decrease of the emission intensity of an upconverter was observed in the green area. This emission corresponds to two luminescence transition of Er³⁺ ions: ${}^2\text{H}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$ and ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^4\text{I}{}_{\mathrm{<mtext>15</mtext><mtext>2</mtext>}}$. A mechanism of the luminescence intensity decrease has been proposed, in which deexcitation of the ${}^4\text{S}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level to the ${}^4\text{I}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ level is caused by a neighbouring Er³⁺ ion being excited to the ${}^4\text{I}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ level.     

Thermoelectric power of (Me4N)2Ag13I15 and (Et4N)2Ag13I15

Thermoelectric power using reversible silver electrodes and electrical conductivity on the compressed pellets of (Me₄N)₂Ag₁₃I₁₅, and (Et₄N)₂Ag₁₃I₁₅ have been measured between room temperature and below 160°C. The results of θ can be expressed by the equations:?θ = 0.115 (10³/T)+0.2905VK^?1 and ?θ = 0.150 (10³/T) + 0.305mV K^?1; and those of conductivity by the equations; σ = 28.7 exp (?0.17eV/kT) ohm^?1cm^?1 and $\text{σ = 216.6 exp (?0.24e}\text{V}\text{kT}\text{)}$ ohm^?1cm^?1; respectively for Me- and Et-electrolytes. The results are discussed and compared with those of previous authors.     

Magnetic field dependent optical dephasing in LaF3:Er3+

Optical dephasing of the 5388 Å transition between the lowest Kramers doublets of the ⁴S_{$\text{3}\text{2}$} and ⁴I_{$\text{15}\text{2}$} multiplets of Er³⁺:LaF₃ has been studied by photon echo, optical phase switching and optical free induction decay. Er³⁺?¹⁹F hyperfine interactions produce dephasing which is two orders of magnitude faster than in previously studied non-Kramers systems, but at high field changes in the spin dynamics result in microsecond dephasing. For the lower Zeeman component of ⁴S_{$\text{3}\text{2}$}, T₂ (=6μs) is independent of H₀ whereas for the upper component the dephasing is rapid and strongly field dependent. This is quantitatively accounted for by spin lattice relaxation of the upper component of ⁴S_{$\text{3}\text{2}$}. Below 20 kG concentration and temperature dependent dephasing due to electron spin diffusion is observed.     

Multiphoton excitation of visible emission in Y2O2S: Er,Yb phosphors by 810 nm excitation

During investigations of anti-Stokes effects in erbium—ytterbium doped yttrium oxysulphide phosphors we have found an excitation of the erbium green emission due to 810 nm radiation (⁴I$\text{15}\text{2}$ → ⁴I$\text{9}\text{2}$ transition), the effect being of a two-photon type. There is also a two-photon excited blue emission (²H$\text{9}\text{2}$ → ⁴I$\text{15}\text{2}$ transition) due to the same radiation. Introduction of ytterbium impurity has a deleterious effect on the above 810 nm excitation, in contrast to its sensitization of the 1000 nm anti-Stokes excitation. To distinguish between various excitation schemes a two-beam excitation technique has been used. Results show that ytterbium inclusions lead to loss of energy from the 810 nm excitation by increasing the probability of downward transitions from the ⁴F$\text{9}\text{2}$ level to ⁴I$\text{11}\text{2}$ and ⁴I$\text{13}\text{2}$ states, reached after onephoton absorption. This effect is indicated by an increase in 1500 nm emission (⁴I_{$\text{13}\text{2}$} → ⁴I_{$\text{15}\text{2}$} with ytterbium concentration.     

Study of the photon spectrum in the decay KS0→π+π−γ

The branching ratio $\text{Λ(}\text{K}{}_{\mathrm{<mtext>S</mtext>}}{}^0\text{→π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{γ)}\text{Λ(}\text{K}{}_{\mathrm{<mtext>S</mtext>}}{}^0\text{→π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{)}$ has been determined to be (2.68±0.15)×10^?3 for photon energies $\text{E}{}_{\mathrm{\gamma }}{}^1$ greater than 50 MeV in the K_S⁰ rest frame. The decay K_S⁰→π⁺π^?γ is found to be dominated by the internal bremsstrahlung transition. The branching rato of a possible direct transition is found to be less than 0.06 × 10^?3 at 90% confidence level for $\text{E}{}_{\mathrm{\gamma }}{}^1\text{> 50}\text{MeV}$.     

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.     

EPR lineshape in ethylenediammonium chloromanganate (II), [C2H10N2] [MnCl4]

The EPR line shape has been measured on a single crystal of ethylene diammonium chloromanganate (II) as a function of field orientation with respect to the expected two dimensional network of manganese ions. The angular variation of the linewidth may be described by the expression δH= α + β(3 cos²δ ? 1)² with α = 20 and β = 4, and the lineshape may be described by I(H ? H₀) ? F [exp (? At ? Bt ln ($\text{t}\text{t}{}_0\text{)]}$ (where F refers to the Fourier transform of the bracketed function) with $\text{|}\text{B}\text{A}\text{| = 1.9 ± 0.8}$.     

A numerical estimate of deviations from the exponential decay law for the transition 2P12→1S12 in hydrogen

The deviations from the exponential decay law of the $\text{2}\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states of the Dirac hydrogen atom with respect to the transition $\text{2}\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→1}\text{S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ are numerically estimated. We find |a₀(t) ? exp(?λt)|?2.5 × 10^?4 for all t, where a₀(t) is the “exact” decay amplitude and λ is a complex constant such that (2Re λ)^?1 is the “natural lifetime” of the $\text{2}\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states with respect to the spontaneous transition to $\text{1}\text{S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$.     

Features of diffractive scattering and the nature of the N1(1400) observed in NN→N(Nπ) reactions at 5.7 GeV/c

The results for the diffractive scattering contribution ($\text{F}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^0$) obtained in a cross channel isospin analysis of the $\text{N}\text{N}\text{→}\text{N}\text{(}\text{N}\text{π)}$ reactions at 5.7 GeV/c are compared with those obtained for other ZN → Z′(Nπ) reactions where Z stands for N, π and the carbon nucleus. The dependence of the diffractive scattering on the mass M_πN and the momentum transfer t seems very weakly related to the nature of Z and the incident momentum.A comparison between amplitudes of the isospin exchange I_ex = 0 and I_ex = 1 leading to $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ production shows that $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1492)}$ and $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1670)}$ are produced essentialy through I_ex = 1.     

νW2 at small ω′ and resonance form factors in a quark model with broken SU(6)

The small ω′ behaviour of F₂^en/F₂^ep and the apparent difference in the q² dependences of the magnetic form factor of the proton and of the transition to Δ⁺(1236) are quantitatively correlated in a model where nucleon consistes of a quarks and a scalar or vector core. The proton and Δ transition form factors suggest that only the scalar core contributes at large q² and small ω′. As a result the ω′ dependence of $\text{F}{}_2{}^{\mathrm{<mtext>en</mtext>}}\text{F}{}_2{}^{\mathrm{<mtext>ep</mtext>}}$ is obtained for ω′ < 3 and predictions for the weak structure functions and polarisation asymmetries at smallω′ are presented. We predict $\text{F}{}^{\mathrm{<mtext>\nu </mtext><mtext>p</mtext>}}\text{F}{}^{\mathrm{<mtext>\nu </mtext><mtext>n</mtext><mtext>\omega \prime \to 1</mtext><mtext>0</mtext>}}$ asymmetries $\text{ω′→1}\text{1}$ and also expect that $\text{G}{}_{\mathrm{<mtext>m</mtext>}}{}^{\mathrm{<mtext>n</mtext>}}\text{G}{}_{\mathrm{<mtext>m</mtext>}}{}^{\mathrm{<mtext>p</mtext>}}\text{→}\text{?1}\text{2}$ as q²→∞.     

Ni2+ emission in MgO,KMgF3, KZnF3 and MgF2

The emission of Ni²⁺ ions in MgO, KMgF₃, KZnF₃ and MgF₂ crystals has been investigated. The fine structure on the bands at about 20 000 cm^-1 and 13 000 cm^-1 has been studied in detail and from this and the excitation spectra these bands are assigned to ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{A}{}_{\mathrm{2g}}$ and ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{T}{}_{\mathrm{2g}}$ transitions respectively.     

2kF and 4kF charge-density waves in TTF0.4TSeF0.6-TCNQ — An X-ray study

In the quasi one-dimensional conductor TTF_0.4TSeF_0.6-TCNQ, it is found that the 2k_F CDW has three-dimensional correlations of relatively long range below the metal-insulator transition temperature ～40K, although the 4k_F CDWs are only one-dimensional in character at all temperatures. This result supports the speculation that the 2k_F CDWs and the 4k_F CDWs are present predominantly on the TCNQ and the fulvalene stacks, respectively. The 2k_F-value of the present material is similar to that of TTF-TCNQ but far from that of TSeF-TCNQ. The change of the value with the concentration of TSeF (or TTF) is nonlinear. The transverse period of the ordered 2k_F CDW along the a-axis is $\text{a}$ just below the transition temperature and becomes 4$\text{a}$ below 34.5K. A discussion is given based on the two-chain model.     

Quasiquadrupolar echoes in solids containing spins-12 triads undergoing hindered reorientation

The spin echo responses to resonant 90⁰-τ-β_φ⁰ rf pulse sequences in solids containing spin-$\text{1}\text{2}$ triads undergoing hindered rotations, are shown to be predicted by a model of dipolar coupled quasiparticles of spin-$\text{3}\text{2}$.     

980 nm激发下Er3+/Yb3+共掺杂ZrO2-Al2O3粉末的上转换发光特性

通过固相反应法制备了Er³⁺/Yb³⁺共掺杂ZrO₂-Al₂O₃粉末的样品，并对样品在980nm激光激发下的上转换发光特性进行了研究.从发射光谱可以发现，在可见光范围内有3个强的发光带，一个位于654nm附近的红光带和两个分别位于545nm、525nm附近的绿光带，分别对应于Er³⁺离子的以下辐射跃迁：⁴F_9/2→⁴I_15/2、⁴S_3/2→⁴I_15/2、 ²H_11/2→⁴I_15/2.其中又以Er³⁺离子的⁴F_9/2→⁴I_15/2跃迁产生的红色荧光辐射最强.对其上转换发光机制进行了分析，发现这三个发光过程都是双光子过程.对样品粉末进行了XRD检测，发现ZrO₂主要以立方相为主，并且计算得到了这种立方结构的晶格常数.Al₂O₃固溶于ZrO₂中，Al³⁺嵌入ZrO₂后产生氧空位，导致ZrO₂晶体的对称性降低，这种结构变化更有利于提高上转换效率，即上转换发光强度增强. 关键词： 3+/Yb³⁺')" href="#">Er³⁺/Yb³⁺ 上转换 2-Al₂O₃')" href="#">ZrO₂-Al₂O₃ 荧光 稀土     

Annealing studies on the absorption spectrum of 41K-atoms trapped in an argon matrix

Argon crystals were doped with 0.2 ppm of ⁴¹K through the nuclear reaction ⁴⁰Ar (n, β^-) ⁴¹K. The absorption spectrum from 300 nm to 800 nm was measured as a function of the annealing temperature. Absorption ← 4²s_{$\text{1}\text{2}$} transition of the free atom could be bands corresponding to the 4²p_{$\text{1}\text{2}$}, _{$\text{3}\text{2}$} ← 4²s_{$\text{1}\text{2}$} and 5²p_{$\text{1}\text{2}$}, _{$\text{3}\text{2}$} ← 4²s_{$\text{1}\text{2}$} transition of the free atom could be observed. The absorption bands depend strongly on the annealing temperature. An increase in the annealing temperature results in a blue shift of the absorption bands.     

Studies of the red anti-stokes emission of erbium ions in the Y2O2S: Er,Yb phosphor system

Excitation of the anti-Stokes red emission radiation from erbium ions by 1000 nm radiation in the Y₂O₂S: Er, Yb system has been investigated using a range of samples with widely varying erbium but fixed ytterbium content. A square law intensity dependence is found favouring the models of Sommerdijk and of Hewes and Sarver. Comparison of Stokes and anti-Stokes excitations of both green and red erbium emissions then eliminates the Hewes and Sarver model. Studies using twin-beam excitation as by Kuroda et al. (1000 nm plus 1500 nm) and over a range of temperatures give evidence that the previous assumption of the non-radiative, multiphonon relaxation between the ⁴I_{$\text{11}\text{2}$} and ⁴I_{$\text{13}\text{2}$} states following the first 1000 nm excitation is not satisfactory and suggest that this transition is radiative (2500 nm radiation).     

Er3+：GdVO4中Er3+离子的光谱参数计算和晶场中能级分裂的讨论

对Er³⁺：GdVO₄样品的光谱参数以及Er³⁺在晶场中能级的分裂情况进行了研究. 首先对样品进行了吸收光谱的测量，接着用Judd-Ofelt理论拟合出了Er³⁺在GdVO₄晶体中的强度参量Ω_t，并由此计算了跃迁的振子强度、自发辐射跃迁速率、荧光分支比和积分发射截面. 通过计算结果可以发现有较多能级之间的跃迁都有大于10^-6的振子强度和大于10^-18cm的积分发射截面，并且具有较高的荧光分支比，特别是²H_11/2→⁴I_15/2，⁴S_3/2→⁴I_15/2，⁴F_9/2→⁴I_15/2和⁴I_13/2→⁴I_15/2等几个强发光能级除了具有较大的振子强度和积分发射截面外还有很好的应用前景，因此也更加值得关注. 最后还利用群论讨论了Er³⁺离子在GdVO₄晶场中各能级的分裂情况并对各Stark子能级的J_z混杂情况进行了分析.