Enhancement of red emission by co-dopant Ln3+ ions in Eu3+ :LaOF nanoparticles

Fluoride nanoparticles of Ln3+(Ln3+=Pr3+,Nd3+,Sm3+,Gd3+,Tb3+Dy3+,Ho3+,Er3+,Tm3+,Yb3+)/Eu3+:LaOF and Eu3+ :LaOF with rhombohedral crystal structure were prepared by a hydrothermal-sintering method. The red fluorescence emission of Eu3+ ions was found to be enhanced with most of the co-dopant Ln3+ ions. Compared with strong fluorescence emission at 610 nm of Eu3+ :LaOF nanoparticles, the enhancement factors was up to ten times in Ln3+(Ln3+ =Gd3+,Dy3+,Tm3+)/Eu3+ :LaOF co-doped nanoparticles. The results show that the asymmetry of the local environment of Eu3+ ion was reduced by co-doping Ln3+ ion into the nanoparticles, and that energy transfer might occur between Eu3+ and codopant Ln3+ ions, which is suggested as the source of the observed fluorescence enhancement.     

Extrinsic luminescence of BaF2: R 3+ crystals ( R 3+ = La3+, Y3+, Yb3+)

This paper reports on a study of cross-luminescence in barium fluoride crystals doped by a variety of impurities (K⁺, Cd²⁺, Y³⁺, Yb³⁺, La³⁺). It is shown that doping of the crystal with a trivalent impurity gives rise to the formation of an additional cross-luminescence band peaking at 7.5 eV, the intensity of this band increasing with increasing impurity concentration. Original Russian Text ? A.S. Myasnikova, E.A. Radzhabov, A.V. Egranov, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 9, pp. 1582–1584.     

纳米晶ZrO2：Eu3＋-Bi3＋的制备及Bi3＋敏化Eu3＋特征发射的研究

采用化学共沉淀法制备了纳米晶ZrO2：Eu3＋-Bi3＋粉体,所制备的纳米晶粉体均能观测到Eu3＋离子的室温特征发射．研究了样品的晶体结构和发光性质．结果表明：经600℃煅烧后得到的纳米晶ZrO2：Eu3＋-Bi3＋粉体的晶相为四方相,经800,950及1100℃煅烧后的样品为四方相和单斜相的混合晶相．Eu3＋离子在四方相中的室温特征发射明显强于在混合相中的发射．Bi3＋离子的掺入对Eu3＋离子的室温特征发射有显著的敏化作用．     

EPR observation of phase transitions in calcium cadmium acetate hexahydrate: Using Mn2+ and Cu2+ ions as probe

Results of temperature dependence of EPR spectra of Mn²⁺ and Cu²⁺ ions doped calcium cadmium acetate hexahydrate (CaCd(CH₃COO)₄·6H₂O) have been reported. The investigation has been carried out in the temperature range between room temperature (～ 300 K) and liquid nitrogen temperature. A I-order phase transition at 146 ± 0.5 K has been confirmed. In addition a new II-order phase transition at 128 ± 1 K has been detected for the first time. There is evidence of large amplitude hindered rotations of CH₃ groups which become frozen at ～ 128 K. The incorporation of Cu²⁺ and Mn²⁺ probes at Ca²⁺ and Cd²⁺ sites respectively provide evidence that the phase transitions are caused by the molecular rearrangements of the common coordinating acetate groups between Ca²⁺ and Cd²⁺ sites. In contradiction to the previous reports of a change of symmetry from tetragonal to orthorhombic below 140 K, the symmetry of the host is concluded to remain tetragonal in all the three observed phases between room temperature and liquid nitrogen temperature.     

Ce3+对Er3+/Yb3+共掺氟磷酸盐玻璃光谱性质的影响

研究了能量接受离子Ce³⁺对Er³⁺上转换发光强度以及Er³⁺在1.5μm附近波段发光性能参数的影响，并从能量匹配及能级结构角度出发对Er³⁺/Ce³⁺间的能量转移机制进行了分析.分析认为，⁴I_11/2能级的Er³⁺通过无辐射能量转移把能量传递给²F_5/2能级的Ce³⁺关键词： 氟磷酸盐玻璃 光谱性质 光纤放大器 3+和Ce³⁺')" href="#">Er³⁺和Ce³⁺     

Optical parameters of Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses and their energy transfers at high temperature

This paper reports that a series of Nd³⁺:Er³⁺:Yb³⁺ co-doped borosilicate glasses have been prepared and their absorption spectra measured. The J--O intensity parameters Ω_k (k=2, 4, 6), spontaneous radiative lifetime τ_rad, spontaneous transition probability A, fluorescence branching ratio β and oscillator strength f_ed of the Nd³⁺ ions at room temperature are calculated based on Judd--Ofelt (J--O) theory. The temperature dependence of the up-conversion photoluminescence characteristics in a Nd³⁺:Er³⁺:Yb³⁺ co-doped sample is studied under a 978 nm semiconductor laser excitation, and the energy transfer mechanisms among Yb³⁺, Er³⁺ and Nd³⁺ ions are analysed. The results show that the J--O intensity parameters Ω₂ increase when the Nd³⁺ concentration of the Nd³⁺:Er³⁺:Yb³⁺ co-doped borosilicate glasses increases. The possibility of spontaneous transition is small and lifetimes are long at levels of ⁴F_5/2 and ⁴F_3/2. The intensity of Nd³⁺ emissions at 595, 691, 753, 813 and 887 nm are markedly enhanced when the sample temperature exceeds 400 K. The reasons being the cooperation of the secondary sensitization from Er³⁺ to Nd³⁺ and the contribution of a multi-phonon.     

Racah and Judd-Ofelt parameters for Pr3+, Nd3+, and Er3+ ions in a laser liquid

The values of the Slater-Condon (F₂, F₄, F₆), Racah (E¹, E², E³) and Lande ξ₄f coefficients the nephelauxetic ratio (β), the bonding parameter (σ), and the Judd-Ofelt intensity (T_λ) parameters have been calculated from the reported absorption spectra of Pr³⁺, Nd³⁺, and Er³⁺ ions in an aprotic solvent SeOCl₂ acidified with antimony pentachloride. The nature of the bonding is suggested to be covalent for praseodymium, neodymium and erbium ions in the laser liquid in view of the magnitude of the respective bonding parameters.     

Minimum ion-ion distance,cross relaxation and excitonic behaviour in Ln3+ stoichiometric materials

Comparison of the self-quenching rates of Nd³⁺(⁴F_3/2) and Tb³⁺(⁵D₃) in two stoichiometric materials LnP₅O₁₄ and LnNa(WO₄)₂, shows opposite behaviour (Ln=lanthanides). For Nd³⁺(⁴F_3/2), LnNa(WO₄)₂ which has a small minimum Ln³⁺ -Ln³⁺ distance ($\text{R}{}_{\min }\text{= 3.9}\text{A}\text{?}$), exhibits a stronger rate than LnP₅O₁₄ ($\text{R}{}_{\min }\text{= 5.2}\text{A}\text{?}$) with respectively a quadratic and a linear concentration dependence. On the contrary, for Tb³⁺(⁵D₃), LnNa(WO₄)₂ exhibits a smaller rate than LnP₅O₁₄ with opposite concentration dependence. Showing that the coherent propagation is negligible, self-quenching is attributed essentially to cross-relaxation with fast or limited incoherent diffusion. Results clearly demonstrate that the existence of a structural isolation is only secondary to energy matching conditions. This in turn confirms the important role of the crystal field strength as exemplified by comparing NaLn(WO₄)₂ and KLn(WO₄)₂.     

Observation of electronic Raman transitions from the transition metal ions Ti3+ and V4+ highly diluted in α-Al2O3

α-Al₂O₃ : Ti³⁺ (300 mass ppm concentration) at 10 K shows two electronic Raman transitions at 38 cm^-1 and 109 cm^-1. The E symmetry of the scattering matrix agrees with the selection rules for transitions between the ground state B_{$\text{3}\text{2}$} and the E_{$\text{1}\text{2}$} of the ground state manifold ²t_2g.α-Al₂o₃ : V⁴⁺ shows two very weak electronic Raman transitions at about 30 cm^-1 and 56 cm^-1 respectively.     

Infrared-to-green upconversion luminescence and mechanism of Ho3+, Nd3+ and Yb3+ ions in oxyfluoride glass ceramics

New oxyfluoride glasses and glass ceramics co-doped with Nd^{3+}, Yb^{3+} and Ho^{3+} were prepared. The upconversion of infrared radiation into green fluorescence has been studied for Nd^{3+}, Yb^{3+} and Ho^{3+} in the transparent oxyfluoride glass ceramics. At room temperature very strong green upconversion luminescence due to the Ho^{3+}: ({}^5F_4, {}^5S_2)→{}^5I_8 transition under 800 nm excitation was observed in the glass ceramics. The intensity of the green upconversion luminescence in a 1mol% YbF_3-containing glass ceramic was found to be about 120 times stronger than that in the precursor oxyfluoride glass. The reason for the highly efficient Ho^{3+} upconversion luminescence in the oxyfluoride glass ceramics is discussed. The upconversion mechanism is also investigated.     

The radiative characteristics of the rovibronic states of the hydrogen molecule: IV. Relative probabilities of the r 3Π g ? , s 3Δ g ? → c 3Π u ± spontaneous transitions of the H2 molecule

A statistical analysis of the available literature data and data obtained in this work on the wave numbers of the lines that appear in triplet-triplet rovibronic transitions of the H₂ molecule was performed. This allowed us to verify and refine the controversial identification of spectral lines and find the optimum rovibronic level energy values for the c ³Π _u ^±, r ³Π _g ⁻, and s ³Δ _g ⁻ states. The ratios between the line strengths of the P, Q, and R branches of the (4dπ)r ³Π _g ⁻, (4dδ)s ³Δ _g ⁻ → (2pπ)c ³Π _u ^± band systems of the H₂ molecule were measured systematically. The calculation results obtained in the Frank-Condon approximation differed substantially (by up to two orders of magnitude) from the experimental data. The dependences of the ratios between rovibronic line strengths of the r ³Π _g ⁻ → c ³Π _u ^± and s ³Δ _g ⁻ → c ³Π _u ^± transitions on the rotational quantum number N′ of the upper level were found to correlate with each other. The deviations of adiabatic theory increase as N′ grows, which is evidence of an important role played by electronic-rotational interactions in the perturbation of transition probabilities. The experimental ratios between the probabilities of rovibronic transitions satisfactorily agree with the results of calculations within the framework of the simple nonadiabatic model taking into account electronic-rotational interaction of radiating adiabatic states in the approximation of pure precession. The dependences of transition probabilities on N′ were obtained for the first time for the first four diagonal bands of the r ³Π _g ⁻, s ³Δ _g ⁻ → c ³Π _u ^± transitions. Original Russian Text ? S.A. Astashkevich, B.P. Lavrov, A.V. Modin, I.S. Umrikhin, 2008, published in Khimicheskaya Fizika, 2008, Vol. 27, No. 2, pp. 22–38.     

Production of recoil ions He^i＋ accompanied by single electron loss of 0.2-7 MeV C^q＋ and 0.25-5 MeV O^q＋ （q = 1- 4） ions

Target ionization accompanied with projectile electron loss is investigated for 0.2-7 MeV C^q＋ （q = 1 - 4） with He and 0.25-5 MeV O^q＋ （q = 1 - 4） with He collisions. For projectile single-electron loss channel, the He double-to-single ionization ratio R is nearly independent of projectile charge state but dependent on the nuclear charge of projectile Zp. The results are analysed with atomic structure qualitatively. So far there have not existed the experimental data comparable with our results, to our knowledge. The ratio R is interpreted in terms of the two-step mechanism. This analysis agrees well with similar experiments in the literature.     

Charge transfer excitation of the Nd3+, Sm3+, Dy3+, Ho3+, Er3+ and Tm3+ emission in CaGa2S4

The excitation spectra of the Nd³⁺, Sm³⁺, Dy³⁺, Ho³⁺, Er³⁺ and Tm³⁺ emission in the sodium-compensated CaGa₂S₄ host lattice, a sulfide with wide band gap, contain an intense band below the absorption edge. Comparison of the energy of its maximum with thermodynamic data and correlations to Jørgensen's refined spin-pairing theory predictions allow one to ascribe this band to a charge transfer transition ending onto 4f orbitals. The irregular variation within the rare earth series contrasts with the monotonic variation of the absorption edge in stoichiometric rare earth sulfides (e.g. NaLnS₂), associated with interband transitions.     

Luminescence of Tb3+ ions in silicate glasses

The optical absorption and photoluminescence emission spectra of terbium doped sodium and lithium aluminium silicate glasses have been measured as a function of terbium concentration. Optical absorption has been measured over the wavelength range from 250 nm to 40 μm and the absorption bands attributed to Tb³⁺ ions have been identified. Luminescence emission occurs in two groups of bands in the blue and in the green. The green ⁵D₄ → ⁷F_J emission is more intense than the blue ⁵D₃ → ⁷F_J. The green luminescence is enhanced at the expense of the blue when the Tb³⁺ ion concentration reaches 0.5 molar%, which corresponds to an ion separation of 20 Å. The green emission is quenched when the Tb³⁺ ion concentration exceeds 5 molar%, corresponding to an ion separation of 9.5 Å. It is concluded that energy transfer from ⁵D₃ to ⁵D₄ levels begins at Tb³⁺ ion separations of 20 Å, and that the process is multipolar. Exchange dipole processes set in at 9.5 Å and quench the green emission. The ion separations at which the two processes occur in silicate glasses are much larger than those at which similar processes set in crystalline material. This enhancement of energy transfer processes in silicate glass is attributed to inhomogeneous broadening of the absorption and emission bands. The detailed structure of the emission bands, particularly that of the ⁵D₄ → ⁷F_6,5,4 doublets, is used to suggest that the Tb³⁺ ions occupy two different sites with rhombohedral and cubic symmetries.     

共掺杂Ce~(3+)调控β-NaLuF_4:Yb~(3+)/Ho~(3+)纳米晶体的上转换荧光发射

在980 nm近红外光激发下,通过共掺杂Ce~(3+)离子调控六方相NaLuF_4:Yb~(3+)/Ho~(3+)纳米晶体的上转换荧光发射.实验结果表明,当掺杂Ce~(3+)离子浓度从0增加到12.0%时,Ho~(3+)离子的上转换荧光发射实现了由绿光向红光的转变,其红绿比提高了近24倍.根据Ho~(3+)离子的能级结构发现,Ho~(3+)离子的红光发射源自~5F_5能级到5I8能级的辐射跃迁,因此要增强红光发射,必须提高该能级粒子数布居.Ho~(3+)与Ce~(3+)离子之间相近的能级差促使它们之间产生了共振交叉弛豫,从而有效地提高了Ho~(3+)离子~5F_5能级的粒子数布居,增强了红光发射.同时对Ho~(3+)离子的上转换调控机理进行讨论,并借助不同的激发策略,进一步证实了Ho~(3+)与Ce~(3+)离子之间相互作用的发生.     

Diffusion-limited energy transfer from Tb3+ → Nd3+ and Tb3+ → Ho3+ in DMSO

The energy transfer phenomenon has been studied from Tb³⁺ → Nd³⁺ and Tb³⁺ → Ho³⁺ in DMSO. A diffusion limited dipole-dipole mechanism of energy transfer is suggested for both systems. At high acceptor concentrations, P_da depends linearly on C² consistent with the Fong and Diestler theory of energy transfer. However, at low acceptor concentrations the observations of time evolutions of Tb³⁺ luminescence decay following flash excitation has enabled us to examine diffusion limited energy transfer from Tb³⁺ to Nd³⁺ and Tb³⁺ to Ho³⁺ in DMSO.     

Study of the optical characteristics of TZLB glass activated by Er3+ and Yb3+ ions

The transmission spectra of glass based on tellurium oxide (TeO₂), of the TeO₂-ZnO-Li₂OBi₂O₃ composition (TZLB), which is highly stable to crystallization, have been measured. The concentration dependences of the luminescence (1.53 μm) intensity and kinetics of erbium ions under 975-nm excitation have been investigated. Based on the experimental results, a fundamental possibility of using TZLB glasses activated by Er³⁺ and Yb³⁺ ions for active elements of fiber and integrated optics is shown.     

Luminescence processes in CsI doped with Na+ and K+ ions

The luminescence bands around 420 nm and 370 nm in CsI:Na and CsI:K have been studied by measuring the temperature dependence of decay times and luminescence and its excitation spectra. The bands are due to singlet+triplet localized excitons and to triplet localized excitons, respectively, at low temperature. Zero field splitting and life time amount to 0.2 meV and 3.3 μs for the 420 nm band, and to 2.1 meV and 1.7 μs for the 370 nm band. Creation processes of 420 nm excitons may not be the same below 40 K and near room temperature.     

Theoretical calculation of of B-like ions： photoionization cross sections N^2＋, O^3＋ and F^4＋

There can be found some notable discrepancies with regard to the resonance structures when R-matrix calculations from the Opacity Project and other sources are compared with recent absolute experimental measurements of Bizau et al [Astron.Astrophts.439 387(2005)] for B-like ions N2+,O3+ and F4+.We performed close-coupling calculations based on the R-matrix formalism for the photoionizations of ions mentioned above both for the ground states and first excited states in the near threshold regions.The present results are compared with experimental ones given by Bizau et al and earlier theoretical ones.Excellent agreement is obtained between our theoretical results and the experimental photoionization cross sections.The present calculations show a significant improvement over the previous theoretical results.     

ESR study of Fe3+ and Mn2+ ions on trigonal sites in ilmenite structure MgTiO3

Electron spin resonance has been observed for Fe³⁺ and Mn²⁺ ions occupying sites with trigonal symmetry in undoped and doped Verneuil-grown crystals of the ilmenite type compound MgTiO₃. At 300 K, the fine structure parameters in the spin Hamiltonian are (in 10^?4cm^?1) D = +844 (± 1), (a? F) = +118 (± 1), a = 69 (± 7) for Fe³⁺ and D = +164 (± 1), (a ? F) = +10.2 (± l), a = 7.0 (± 1) for Mn²⁺. These values are compared with literature data for Fe³⁺ and Mn²⁺ in other oxides, especially Al₂o₃, with particular reference to the recent “superposition” theory of the effect of a trigonal distortion. From the orientation of the axes of cubic pseudosymmetry of the spin Hamiltonian, and with the assumption that a has the same sign for both ions, it is proposed that Fe³⁺ and Mn²⁺ occupy the same octahedral site, namely the Mg²⁺ site. Anomalous line splittings observed for one sample were attributed to twinning on (0001) or {1120} planes.