玻璃中Nd3+离子4F3/2态的多声子弛豫及电子-声子相互作用

本文通过在不同温度下测定Nd³⁺离子⁴F_3/2态的荧光和寿命的方法,确定了Nd³⁺离子⁴F_3/2态的多声子弛豫率对温度的关系,并根据多声子理论和红外振动谱对过程进行了理论拟合,研究了五种玻璃⁴F_3/2态的多声子过程,确定了过程所涉及的声子能量和声子数目,分析了多声子弛豫率与基质性质的关系,进一步在钕玻璃中检验了多声子理论。     

Single color upconversion emission in Ho/Yb and Tm/Yb doped P2O5-MgO2-Sb2O3-MnO2-AgO glasses

The Ho³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ doped P₂O₅-MgO₂-Sb₂O₃-MnO₂-AgO glasses were prepared by high temperature melting method. Under a 975 nm laser diode (LD) excitation, the single red and single blue upconversion (UC) emissions were observed in Ho³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ doped samples, respectively. By studying the spontaneous radiative and multiphonon relaxation probabilities, we find that the multiphonon relaxation probability of ⁵I₆ (Ho³⁺) state is very large (1.39 × 10⁶ s^− 1), which is helpful to the population of ⁵I₇ state. The multiphonon relaxation probability of ³H₅ and ³F_2,3 (Tm³⁺) is also very large, which results in lots of population in ³F₄ and ³H₄ states. The results are that the red UC emission of Ho³⁺ and the blue UC emission of Tm³⁺ are stronger.     

Stimulated emission and radiative properties of Nd ions in barium fluorophosphate glass containing sulphate

Spectroscopic properties of Nd³⁺ in barium fluorophosphate glassy matrix containing sulphate have been analysed by fitting the experimental data with the standard Judd-Ofelt theory. Various spectroscopic parameters viz. radiative transition probabilities, radiative decay time, fluorescence branching ratios, electric dipole line strengths, stimulated emission cross sections and optical gain of the principal fluorescence transition from the ⁴F_3/2 metastable level are obtained. Results show that addition of sulphate to the fluorophosphate matrix will enhance the fluorescence spectral properties of Nd³⁺ considerably. Quantum efficiency of the ⁴F_3/2 emission is found to be higher than that of fluorophosphate glasses and stimulated emission cross section of the ⁴F_3/2→⁴I_11/2 transition is the highest among all reported values. Quantitative estimation of the non-radiative processes such as multiphonon relaxation and quenching by water content was carried out and the results show that the water content is below the critical level for optimum laser performance.     

Optical emission spectroscopy of Ar-N2 mixture plasma

Optical emission spectroscopy measurements are presented to characterize the different excitation and ionization processes of both atomic and molecular species in Ar-N₂ mixture plasma under different discharge conditions. Particularly, the emission intensities of nitrogen (0-0) band of second positive system at 337.1 nm and (0-0) band of first negative systems at 391.4 nm are used to determine the dependence of their radiative states on argon fraction in the mixture. It is observed that the addition of argon gas influences the radiative states differently due to their different populating mechanisms. The results demonstrate that the addition of argon to nitrogen plasma remarkably enhance the population of N₂(C³Π_u) radiative state through Penning excitation involving argon metastable states. The electron temperature is determined from Ar-I spectral line intensities, using Boltzmann's plot method and is found to depend on argon fraction in the mixture.     

Influence of borate content on the radiative properties of Nd ions in fluorophosphate glasses

Spectroscopic properties of Nd³⁺ in barium fluoroborophosphate glassy matrix have been analyzed by fitting the experimental data with the standard Judd-Ofelt theory. Various spectroscopic parameters viz. radiative transition probabilities, radiative decay time, fluorescence branching ratios, electric dipole line strengths, stimulated emission cross-sections and optical gain of the principal fluorescence transitions from the ⁴F_3/2 metastable level are obtained. Results show that addition of borate content to the fluorophosphate matrix will reduce the fluorescence spectral properties of Nd³⁺. However, the radiative properties of the present fluoroborophosphate glassy matrix are found to be well improved over that of pure borate and phosphate matrix and is attributed to the influence of fluorine content in the glassy matrix. The changes in the position and the Judd-Ofelt intensity parameters are correlated with the structural changes in the host glass matrix. The shift of the hypersensitive band shows that the covalency of the rare earth to oxygen bond increases with the increase of Na₂O content. This covalency effect and the formation of the BO₄ groups with the addition of Na₂O content are responsible for the increase in the radiative properties of the present system. Quantitative estimation of the non-radiative processes such as multiphonon relaxation and quenching by water content was carried out and the results show that both are below the critical level for optimum laser performance.     

QUANTUM EFFICIENCY AND MULTIPHONON NONRADIATIVE TRANSITION OF Er3+ IONS IN FLUORIDE GLASS

Optical absorption, emission and excitation spectra, lifetimes of ⁴S_3/2 state and ⁴F_9/2 state from 10K to 500K, and Raman spectra were measured for Er³⁺ ions in fluoride glass. The radiative transition probabilities were calculated on the basis of Judd-Ofelt theory. The nonradiative transition probabilities and the quantum efficiencies were determined by calculating the difference between the measured lifetimes and the calculated radiative transition probabilities. The temperature dependence of nonradiative transition provavility was investigated using the Huang-Rhys theory of multiphonon relaxation , in which two kinds of phonons as well as the parameter s were taken into consideration. A fairly good agreement of the theoretical calculation with the experimental results has been obtained. The value of s is estimated and the effect of s is discussed.     

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).     

钕玻璃的光谱性质

本文分析了Nd³⁺在玻璃中的stark分裂情况,描写了确定荧光能级的实验方法,并给出了钕在四种硅酸盐玻璃中亚稳态和基态能级Stark分裂的实验结果。同时,对十三种不同成份的玻璃,通过光谱实验确定了Nd^{3+ 4}F_3/2态的辐射和无辐射跃迁速率,受激发射截面σ,辐射量子效率η,荧光分支比β和亚稳态寿命τ等激光常用参数。并对实验结果进行了讨论。 关键词：     

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.     

Investigation on luminescence properties of Nd ions in alkaline-earth titanium phosphate glasses

Nd³⁺ ions doped alkaline-earth titanium phosphate glasses were prepared by using the conventional melt quenching method. Absorption spectra were recorded and oscillator strengths of the transitions were calculated using area under the absorption bands. The energy level analysis was carried out by using free-ion Hamiltonian model. The three host dependent Judd-Ofelt intensity parameters, Ω_λ (λ = 2, 4, and 6) were used to elucidate the structure of glassy matrix around Nd³⁺ ion as well as to determine the ⁴F_3/2 metastable state radiative properties such as radiative transition probabilities, branching ratios and radiative lifetimes. The decay curves of all the three glasses show single exponential behavior. The discrepancy between the experimental and calculated lifetimes of emitting level was attributed to multiphonon relaxation. The achieved high quantum efficiencies for the ⁴F_3/2 level indicate efficient laser emission at 1.06 μm in these glass systems.     

Spectroscopic study of erbium-activated crystals of double calcium yttrium fluoride Ca<Subscript>0.89</Subscript>Y<Subscript>0.11</Subscript>F<Subscript>2.11</Subscript>:Er<Superscript>3+</Superscript>: I. Intensity of spectra and luminescence kinetics

Ca_0.89Y_0.11F_2.11:Er³⁺ (CYF:Er) crystals with an erbium content of 1–15 at % have been grown. The optical spectra and luminescence kinetics of CYF:Er crystals have been investigated at low (～5 K) and room temperatures. Based on an analysis of the absorption spectra at low temperature, the structure of Stark splitting of erbium levels in CYF:Er crystals is determined. Room-temperature absorption spectra are used to calculate the spectra of absorption cross sections and oscillator strengths of transitions from the erbium ground state to excited multiplets. It is shown that the absorption spectrum of CYF:Er crystals contains broad bands in the ranges of 790–815 and 965–980 nm, which correspond to the range of emission of laser diodes. For the band peaking near 967 nm, the peak absorption cross section is σ _abs ^max = 2.7 × 10^?21 cm². The intensity parameters are determined by the Judd-Ofelt method to be Ω₂ = 1.39 × 10^?20, Ω₄ = 1.34 × 10^?20, and Ω₆ = 2.24 × 10^?20 cm². The radiative transition probabilities, radiative lifetimes, and branching ratios are calculated with these values. The luminescence decay kinetics from excited erbium levels upon selective excitation is investigated and the experimental lifetimes of the 4F _9/2, ⁴ S _3/2, and ⁴ G _11/2 radiative erbium levels are determined. The dependences of multiphonon relaxation rates on the energy gap in CYF:Er crystals are obtained. The rates of nonradiative multiphonon relaxation from radiative erbium levels are determined.     

UV-violet emission properties of 2F(2)5/2 energy level of Nd3+ ions in ZBLAN glass

In this work the short-wavelength emission properties are investigated for the highest observed 4f metastable energy level ²F(2)_5/2 of Nd³⁺ ions in fluorozirconate ZBLAN glass. Various dopant concentrations, ambient temperatures and excitation conditions have been considered throughout the study. Distinct spectral features were observed under pulsed and cw excitation at 514 nm. In particular, pulsed pumping enabled recording of ²F(2)_5/2 emission spectra, not observable under CW excitation, as well as the level’s fluorescence decay dynamics and its evolution with temperature and dopant concentration. According to the best of the authors’ knowledge, neither the fluorescence lifetime of ²F(2)_5/2 of Nd³⁺ in ZBLAN, nor its concentration dependent evolution were reported before.     

Decay pathway and high-temperature luminescence of Eu in Ca2Gd8Si6O26

The temperature-dependent luminescence of Eu:Ca₂Gd₈Si₆O₂₆ and its decay pathways are investigated in order to assess the utility of the material as a thermometric phosphor. Non-radiative decays are found to compete with radiative processes even at room temperature. A decay pathway involving decay through charge-transfer states is proposed based on the decay profiles of emissions from ⁵D₁ and ⁵D₀ levels and on the temperature sensitivity of the spectra as observed after excitation by several wavelengths. The implications of this on solid-state lighting are also discussed.     

Tm3+/Yb3+共掺铋碲酸盐玻璃中的高效蓝色上转换荧光

制备了高折射率Tm³⁺/Yb³⁺共掺杂铋碲酸盐玻璃，利用棱镜耦合法测量出玻璃在632.8和1550nm波长处的折射率分别为2.0365和1.9795. 对玻璃的吸收、荧光和红外透过光谱展开了测试与分析，根据Judd-Ofelt理论对吸收光谱进行拟合，求得Tm³⁺的振子强度参数Ω_t(t=2，4，6)分别为3.90×10^-20, 2.03×10^-20和9.03×10^{-2 关键词： 3+}/Yb³⁺共掺')" href="#">Tm³⁺/Yb³⁺共掺 铋碲酸盐玻璃 光谱参数 上转换荧光     

Spectroscopic properties and exicted-state relaxation dynamics of Er3+ in LiNbO3

Nonequivalent Er³⁺ sites in LiNbO₃ crystals have been evidenced by low-temperature optical absorption measurements. The radiative transition rates for the ⁴ S _3/2, ⁴ F _9/2, ⁴ I _9/2, ⁴ I _11/2, and ⁴ I _13/2 levels have been evaluated by the Judd-Ofelt method, and the contribution of multiphonon relaxation to the decay of excited states has been estimated. The quantum efficiency of the ⁴ I _11/2 level has been estimated to be 6% only, thus the excitation of levels lower than ⁴ S _3/2 is expected to populate efficiently the ⁴ I _13/2 level.     

Radiative and non-radiative transitions in ErP5O14 single crystals

The radiative and non-radiative transitions from excited states of ErP₅O₁₄ were studied on the basis of the Judd-Ofelt theory and experimental data. It was shown that the non-radiative relaxations, predominantly multiphonon emission, are very effective in the depopulation of excited states of erbium in erbium pentaphosphate crystals. The concentration quenching of erbium fluorescence is found to be small.     

ZnS:Ho3+的辐射跃迁和无辐射过程

本工作研究了Ho³⁺离子在宽禁带半导体ZnS中的辐射跃迁和无辐射过程。用发射谱线的积分光强和激发态寿命获得ZnS:Ho³⁺的强度参数Ω_λ,同时计算了九个激发态的辐射跃迁几率和能级寿命。另外,通过在不同温度下测定Ho³⁺离子⁵G₆,³K₈,⁵F₂,⁵F₃和⁵S₂(⁵F₄)能级的发射光强和寿命的方法,研究了这几个激发态间的无辐射过程,其中⁵G₆,³K₈,⁵F₂和⁵F₃这四个能级是处于热平衡状态,而⁵F₃与⁵S₂(⁵F₄)能级间存在五个声子((1/n)ω_Lo=351cm^-1)参与的多声子弛豫过程。 关键词：     

Ni2+:BeAl2O4晶体发光性质的研究

用时间分辨的激光诱导荧光光谱方法测量了10—300K温度范围内Ni²⁺:BeAl₂O₄晶体的红外荧光光谱和荧光寿命。通过荧光寿命的温度变化特性分析,得出³T_2g态的内禀辐射衰减寿命为123±7.2μs。无辐射弛豫的Mott激活能为1147cm^-1,并导出了此晶体发光量子效率随温度的变化关系式。Ni²⁺:BeAl₂O_{4关键词：}     

A redetermination of the lifetime of the 4s 5s (3S1) level in Ca by high-rate electron—photon stepwise pulse excitation

The radiative lifetime of the 4s 5s (³S₁) level in Ca was measured using two-step excitation of atoms in a beam which traverses a cold-cathode Penning discharge, where, by electron impact the atoms are excited to the metastable 4s 5p (³P_{2, 1, 0}) states. Immediately thereafter, the beam is crossed with a pulse-modulated cw dye laser beam to populate the final state selectively. Using a pulse-modulation frequency of 0.5 MHz, a preliminary value of 12.4 ± 0.5 ns was obtained with a statistical error of 0.4%. The wide limits of systematic error reflect an assumed uncertainty in the excitation function and possible distortion in the fluorescence decay requiring further study.