Characterization of host-lattice emission and energy transfer in BaMgAl10O17:Eu

Host-lattice emission, energy transfer and degradation processes are characterized in undoped and Eu-doped BaMgAl₁₀O₁₇. Undoped BaMgAl₁₀O₁₇ exhibits a broad emission centered at 265 nm when excited at wavelengths shorter than 190 nm. This emission is assigned to exciton recombination at Ba-O groups in the cation layer of the lattice. The emission exhibits excellent overlap with the excitation band of Eu²⁺ in this host, providing a means of host-to-activator energy transfer in the doped phosphor. The exciton emission is relatively stable to thermal damage, but undergoes a peak shift and significant decrease in intensity after exposure to VUV radiation. Heating of VUV-damaged materials in air leads to some repair of the spectral properties.     

Photoionization cross-section measurements from the 2p, 3d and 3s excited states of lithium

The photoionization cross-sections from the 2p²P_{1/2, 3/2}, 3d²D_{3/2, 5/2} and 3s²S_1/2 excited states of lithium have been measured at different ionizing laser wavelengths, above the first ionization threshold. The experiments are performed by using a thermionic diode working in the space charge limited mode and the cross-sections are measured by employing the saturation technique. By changing the ionization photon energy, a smooth frequency dependence of the cross-sections has been observed for the 2p and 3d states. The cross-section from the 3s excited state has been measured at a single photon energy. The measured values of the photoionization cross are compared with the available data.     

BCl3振动激发弛豫的红外吸收研究

本工作用红外双共振技术测量了BCl₃分子的振动激发态吸收光谱。观察了分子间的多种弛豫过程及能量转移过程。得到关系式Pτ_V-V^(11BCl₃)=3微秒·托。观察到径向声波对双共振信号的调制,声速为2×10⁴厘米/秒,与计算值相符。 关键词：     

Dynamics of resonant energy transfer in a cold Rydberg gas

We investigate excitation transfer and migration processes in a cold gas of rubidium Rydberg atoms. Density-dependent measurements of the resonant population exchange for atoms initially excited into the 32P_3/2(|m_J|=3/2) state are compared with a Monte Carlo model for coherent energy transfer. The model is based on simulations of small atom subensembles involving up to ten atoms interacting via coherent pair processes. The role of interatomic mechanical forces due to the resonant dipole-dipole interaction is investigated. Good agreement is found between the experimental data and the predictions of the model, from which we infer that atomic motion has negligible influence on the energy transfer up to Rydberg densities of 10⁸ cm^-3, that the system has to be described in terms of many-body dynamics, and that the energy transfer preserves coherence on microsecond timescales.     

Diffusion of excited state molecules in FIR- and CO2-lasers

Both standing waves in laser oscillators and spatially inhomogenous cross sections of laser beam and pumprate cause a non-uniform distribution of excited state molecules in longitudinal and transversal direction, respectively. This spatial hole burning however is smoothed by diffusion of the excited molecules. The effect of diffusion is investigated theoretically for an optically pumped far infrared laser as well as the corresponding CO₂ pump laser. It is found, that the remaining spatial hole burning in the direction of wave propagation is negligible within CO₂ lasers but not within FIR lasers. Concerning the transversal direction it can be shown that in the FIR laser diffusion takes no effect, whereas the transversal distribution of the excited molecules in the CO₂ laser is significantly influenced by diffusion.FIR ring lasers avoid longitudinal spatial hole burning, which leads to the common assumption that they use the active medium more efficient than conventional standing wave lasers, hence delivering higher output powers. This expected advantage is levelled out to a great extent by diffusion.     

强红外场作用下BCl3振动态传能动力学研究

基于文献[1],本工作在较高泵浦激光能通量范围,测量并研究了BCl₃分子振动激发v_3吸收谱及时间演变,观察了v₃激发弛豫的几种能量转移过程,以及对泵浦激光能量BCl₃气压等参数的依赖关系。表明泵浦光脉冲产生一个振动态非热分布的系综,转动能量转移对引起这种非热分布有重要作用。用简化碰撞动力学模型讨论了BCl₃振动激发吸收谱的演变过程,得到振动态再分布的简单关系;Pτ_v-v≌c/K′(T_v,T₀,q)和等效振动温度、平均吸收光子数的分析表达式,与实验结果定性地符合。 关键词：     

Intra-center energy transfer dynamics in Cd1−xMnxTe semi magnetic semiconductors

Intra-center luminescence of Cd_1?xMn_xTe semi magnetic semiconductors under low excitation density was investigated both experimentally and by Monte-Carlo simulation. Experimental time-resolved spectra of 2 eV-band under different photon energy for excitation were used. The approach revealed that Mn²⁺–Mn²⁺excitation energy transfers take place by means of resonant dipole–dipole interaction. Besides energy transfer dynamics is strongly influenced by hopping-assisted quenching. Having been intra-center excitation selective-, mixed- and non-selective types of excitation are proved to occur if photon energy for excitation is increased. This is originated from overlapping of ⁴T₁- and ⁴T₂-states. Under inter-band excitation it was established that Mn²⁺-ion excitation takes place with the aid of excitonic energy transfer, with excitation energy being centered at exciton energy. Under temperature rise the transfer rate vigorously enhances due to great increase of overlap integral of Mn²⁺- ions' side-bands. The quenching is proved to be limited in accordance with existing theory. Inhomogeneous broadening diminishes as a result of fast fluctuation rate of excited ions' energy.     

Optical losses in YVO4: RE (RE = Nd3+, Er3+, Tm3+) laser crystals

The relevance of processes contributing to depletion of pump and upper laser levels has been assessed based on experimental data obtained during measurement of excited state absorption, steady state emission and dynamics of excited states as a function of excitation power and activator concentration. It has been concluded that the excited state absorption in YVO₄: Nd and YVO₄: Er is not significant except for that from the ⁴ I _11/2 level of Er³⁺. In these systems, the interionic processes are dominant. In particular, the reported decrease of the YVO₄: Er laser slope efficiency when the Er³⁺ concentration increased from 0.5 to 1 at % is due mainly to the up-conversion by energy transfer from the pump level and upper laser level. Excited state absorption cannot contribute to depletion of excited states involved in the ³ F ₄-³ H ₆ laser operation near 1800 nm in the YVO₄: Tm crystal. However, the heavy doping required to enhance the cross-relaxation process which feeds the upper laser level brings about the migration-accelerated energy transfer to energy sinks.     

Enhanced luminescence of Dy in Y3Al5O12 by Bi co-doping

In the present paper, phosphors with the composition Y_3−x−yAl₅O₁₂:Bi³⁺_x, Dy³⁺_y were synthesized with solid state reactions. The luminescence properties of Bi³⁺ and Dy³⁺ in Y₃Al₅O₁₂(YAG) and the energy transfer from Bi³⁺ to Dy³⁺ were investigated in detail. Bi³⁺ in YAG emits one broad band peaking at 304 nm which can be ascribed to the transition from excited states ³P_{0, 1} to ground state ¹S₀. Dy³⁺ in YAG emits two groups of peaks around 484 and 583 nm, respectively, which can be ascribed to the transitions from excited state ⁴F_9/2 to ground states ⁶H_15/2 and ⁶H_13/2. The co-doping of Bi³⁺ enhances the luminescent intensity of Dy³⁺ by ∼7 times because Bi³⁺ can transfer the absorbed energy to Dy³⁺ efficiently. The mechanism of energy transfer was also discussed.     

甲醛的态选择性多光子电离研究

我们在XeCl准分子激光多光子电离甲醛分子的研究中,获得了甲醛经过2+1和2+2光子共振激发过程而产生的母体离子和高能离解通道的离子CO⁺。在电子轰击和单光子电离中占优势的低能阈离解通道离子HCO⁺,由于态选择性激发的结果而未出现。 关键词：     

Multiplication of electronic excitations in nanophosphors Lu2O3:Eu and Lu2O3:Tb

Luminescence properties of Lu₂O₃:Eu³⁺ and Lu₂O₃:Tb³⁺ nanocrystalline powders with the particle size varying from 46 to 6 nm were studied under excitation by synchrotron radiation in the photon energy range (up to ∼22.5 eV) covering the region where the processes of multiplication of electronic excitation occur. It was found that the excitation spectra of Tb³⁺ emission from all Lu₂O₃:Tb³⁺ nanopowders have similar behavior, whereas the shape of the excitation spectra of Eu³⁺ emission from Lu₂O₃:Eu³⁺ nanopowders strongly depends on the particle size. The difference in the behavior of Lu₂O₃:Eu³⁺ and Lu₂O₃:Tb³⁺ nanophosphor systems was explained by different mechanisms of the energy transfer from the host to Eu³⁺ or Tb³⁺ ions (either the hole or electron recombination mechanism, respectively), which are differently influenced by losses of electronic excitations near the particle surface.     

Ion beam mixing induced by electronic energy deposition in Fe-Si multilayers

Abstract

Spectroscopic properties of Ce³⁺ ions in GdAlO₃ crystal are presented. At least three Ce³⁺ nonequivalent centres (multisites) are present in this crystal. Energy transfer from the Ce³⁺ main in the UV emitting centres to the Ce³⁺ green emitting centres is observed. Ce³⁺ fluorescence decays are either fast (1.5–20 ns) or slower due to complicated processes of energy transfer and migration (Ce³⁺)_i → (Gd³⁺)_n-steps → (Ce³⁺)_j (energy transfer through Gd³⁺ sublattice).     

Two-photon fluorescence spectrum in an atom + dielectric microsphere system

A strong resonant interaction of a two-level atom with a dielectric microsphere is studied on the basis of quantum electrodynamics. The initial condition considered is one in which the atom is initially excited and the resonant mode of the microsphere has been excited by a single photon. The spectrum of two emitted photons depends strongly on the method used to excite the microsphere, i.e., on the spatial distribution of the photon energy. The most characteristic feature of the two-photon fluorescence spectrum is a strong energy correlation of the emitted photons. This correlation is expressed in the fact that the energies of the emitted photons are related by the equation of an ellipse (ω+ω ₂−2ω _vA )²+3(ω ₁−ω ₂)²= 4Ω _Rabi ² . The relation between the results obtained and the predictions of the theory of dressed states is discussed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 192–197 (10 August 1999)     

Luminescence properties of NaGd(PO3)4:Eu3+ and energy transfer from Gd3+ to Eu3+

The luminescence properties of polyphosphates NaEu _x Gd_(1?x)(PO₃)₄ (x = 0–1.00) and the energy transfer from Gd³⁺ to Eu³⁺ were studied. In undoped NaGd(PO₃)₄ sample, the photon cascade emission of Gd³⁺ was observed under ⁸S_7/2 → ⁶G_J excitation (201 nm) in which the emission of a red photon due to ⁶G_J → ⁶P_J transition is followed by an ultraviolet photon emission due to ⁶P_J → ⁸S_7/2 transition. When part of Gd³⁺ ions in the host NaGd(PO₃)₄ were substituted by Eu³⁺ ions, the NaGd(PO₃)₄:Eu³⁺ sample showed intensive red emission under 172-nm vacuum-ultraviolet (VUV) excitation which is suitable for mercury-free fluorescent lamps and plasma display panel applications. Based on the VUV–visible spectroscopic characteristics and the luminescence decay properties of NaGd(PO₃)₄:Eu³⁺, it was found that the quantum cutting by a two-step energy transfer from Gd³⁺ to Eu³⁺ can improve the red emission of Eu³⁺ ions under VUV excitation but only a part of the excitation energy in the excited ⁶P_J states within Gd³⁺ ions can be transferred to Eu³⁺ ions for its red emission, and the nonradiative energy transfer efficiencies from the excited ⁶P_J states within Gd³⁺ to Eu³⁺ were calculated.     

Monochromatic blue-green and red emission of rare-earth ions in MgGa2O4 spinel

Pr³⁺-activated blue-green phosphor and Eu³⁺-activated red phosphor hosted in MgGa₂O₄ spinel have been prepared by a gel-assisted high-temperature calcination process, respectively. Both anion and cation vacancies in the host were formed by decreasing the Mg concentration in the reaction source. The induced vacancies provide possibility of the accommodation of the doped rare-earth ions with larger atomic size in the highly symmetrical spinel structure. Due to the efficient energy transfer from the spinel host to the sole 4f sub-level of the doped rare earths, monochromatic emissions with high efficiency can be obtained to allow the phosphors to find applications in solid-state laser device and other phosphors excited under low energy. The corresponding spectroscopic transition mechanism has been proposed in this work.     

改进的反Stokes能量传递对ErP5O14非晶中荧光动力学研究的影响

本文通过建立不同浓度五磷酸盐非晶材料(Er_xLa_1-xP₅O₁₄)动力学过程的速率方程,特别是引入了改进系数exp{hc _k/kT}以区别能量传递Stokes过程和反Stokes过程,分别对Er_0.01La_0.99P₅O₁₄,Er_0.1La_{关键词： 反Stokes能量传递改进系数 动力学过程 五磷酸盐非晶 红外量子剪裁}     

Radiative electron-attachment spectra of O3 and SO2

Several aspects of radiative electron-attachment processes are discussed and the corresponding photon energy spectra computed for O₃ and SO₂. In both cases the vibrational stretching mode is significantly excited. The calculated electron attachment spectrum of SO₂ is compared with the laser photo-detachment spectrum of SO₂ ^-. The computed electron affinities and changes in geometry between natural and negative ion are in good agreement with the experimental data.     

A new synthetic pathway of Sr2CeO4 phosphor and its characterization

A blue-white emitting Sr₂CeO₄ phosphor was synthesized via a simple sol-gel poly vinyl alcohol (PVA)-complexing process using strontium nitrate and cerium nitrate as raw materials. The samples were characterized by TG/DTA, XRD, FTIR, SEM and photoluminescence spectroscopy. The X-ray diffraction study confirms the structure of the system to be orthorhombic. The emission spectra when excited at 267 nm peaks at ∼470 nm. The emission band is assigned to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce⁴⁺ ion. The Commission International de l'Eclairage (CIE) co-ordinates for the Sr₂CeO₄ sample were also calculated.     

Luminescence and energy transfer in La2O3–Nb2O5–B2O3:M3+ (M=Bi,Eu, Dy) glasses

The luminescence and energy transfer processes in La₂O₃–Nb₂O₅–B₂O₃:M³⁺ (M=Bi, Eu, Dy) glasses were investigated using luminescence spectroscopy (excitation and emission, down to 4.2 K) and decay time measurements at room temperature. The observation of niobate luminescence implies a considerable degree of short- and intermediate-range order in these glasses. Energy transfer from the niobate groups to the lanthanide ions was observed for Eu³⁺, but not for Dy³⁺, suggesting that the energy transfer process occurs to the charge-transfer state of the Eu³⁺ ion, rather than to its f-levels. Inter-Eu³⁺ energy transfer was negligible in the concentration range investigated (up to 3 mol%). In contrast, cross-relaxation processes between Dy³⁺ ions were active at concentrations as low as 0.5 mol%. In the Bi³⁺ doped glasses the energy transfer was observed from the Bi³⁺ excited levels to the oxygen deficient niobate groups.     

Processes of the excitation energy migration and transfer in Ce-doped alkali gadolinium phosphates studied with time-resolved photoluminescence spectroscopy technique

Spectral-kinetic characteristics of Gd³⁺ and Ce³⁺ luminescence from a series of Ce³⁺-doped alkali gadolinium phosphates of MGdP₄O₁₂ type (M=Li, Na, Cs) have been studied within 4.2-300 K temperature range using time-resolved luminescence spectroscopy techniques. The processes of energy migration along the Gd³⁺ sub-lattice and energy transfer between the Gd³⁺ and Ce³⁺ ions have been investigated. Peculiarities of these processes have been compared for MGdP₄O₁₂ phosphate hosts with different alkali metal ions. A contribution of different levels from the ⁶P_j multiplet of the lowest Gd³⁺ excited state into the energy migration and transfer processes has been clarified. The phonon-assisted occupation of high-energy ⁶P_{5/2, 3/2} levels by Gd³⁺ in the excited ⁶P_j state has been revealed as a shift of Gd³⁺⁶P_j→⁸S_7/2 emission into the short-wavelength spectral range upon the temperature increase. The relaxation of excited Gd³⁺ via phonon-assisted population of Gd³⁺⁶P_5/2 level (next higher one to the lowest excited ⁶P_7/2) is supposed to be responsible for the rise in probability of energy migration within the Gd³⁺ sub-lattice initiating the Gd³⁺→Ce³⁺ energy transfer at T<150 K, whereas further intensification of Gd³⁺→Ce³⁺ energy transfer at T>150 K is explained by the increase in probability of Gd³⁺ relaxation into the highest ⁶P_3/2 level of the ⁶P_j multiplet. An efficient reversed Ce³⁺→Gd³⁺ energy transfer has been revealed for the studied phosphates at 4.2 K.