MULTIPHONON ORBIT-LATTICE RELAXATION OF EXCITED STATES OF RARE-EARTH IONS IN CRYSTALS
MULTIPHONON ORBIT-LATTICE RELAXATION OF EXCITED STATES OF RARE-EARTH IONS IN CRYSTALS
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晶体中稀土离子激发态的多声子轨道-晶格弛豫
DOI：
10.1103/physrev.174.429
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发表时间：
1968-01-01
期刊：
影响因子：
--
通讯作者：
MOOS, HW
中科院分区：
文献类型：
--
作者：
RISEBERG, LA;MOOS, HW
对晶体中稀土离子激发态的多声子轨道-晶格弛豫进行了系统的研究。通过测量激发态荧光寿命和多声子弛豫量子效率，确定了以下晶体的纯多声子跃迁速率：(1)La br3: Nd 3+， La br3: Dy 3+和La br3: Ho 3+；(2) La f3: er3 +和La f3: Ho 3+；(3) Sr f2: ho3 +和Sr f2: er3 +；(4) y2o3: er3 +和y2o3: ho3 +。使用荧光相移技术在近红外和使用脉冲激发技术在可见光区域测量寿命。测量在4.2 K下进行，以确定自发多声子跃迁率，以及在更高的温度下。用一个理论模型拟合了温度依赖性，该模型涉及由热填充声子模式引起的声子受激发射。这些结果表明，衰变涉及高能光学声子的发射，并且发生在声子谱中能量守恒和截止所允许的最低阶。发现自发跃迁速率与跃迁到终端能级的能量，即与能隙有系统的指数依赖关系。这种行为被解释为轨道-晶格微扰展开的简单收敛。随着这些高阶过程中相互作用声子模式和原子能级的精确特征的平均，给定晶格内唯一的关键参数是能量间隙，即过程的顺序。利用光声子截止能量对能隙进行归一化，提取了对阶数的依赖关系。给定阶数的收敛速度和收敛速度反映了轨道-晶格相互作用的强度。给定主体的相对行为可以通过其已知的晶体性质来解释，特别是声子频率分布函数和静态晶体场。在y2o3中观察到的序依赖性表明，对于具有强共价的晶体，轨道-晶格相互作用相对较弱。
A systematic study has been made of multiphonon orbit-lattice relaxation of excited states of rare-earth ions in crystals. By measuring both excited-state fluorescence lifetimes and multiphonon relaxation quantum efficiencies, pure multiphonon transition rates were determined for the following set of crystals:(1) La Br 3: Nd 3+, La Br 3: Dy 3+, and La Br 3: Ho 3+;(2) La F 3: Er 3+ and La F 3: Ho 3+;(3) Sr F 2: Ho 3+ and Sr F 2: Er 3+; and (4) Y 2 O 3: Er 3+ and Y 2 O 3: Ho 3+. Lifetimes were measured both in the near infrared using the fluorescence phase-shift technique, and in the visible region using pulse-excitation techniques. Measurements were performed at 4.2 K to determine spontaneous multiphonon transition rates, as well as at higher temperatures. The temperature dependences were fitted with a theoretical model involving the stimulated emission of phonons due to the thermally populated phonon modes. These results indicate that the decay involves the emission of high-energy optical phonons and occurs in approximately the lowest order permitted by energy conservation and cutoff in the phonon spectrum. The spontaneous transiton rate was found to have a systematic exponential dependence on the transition energy to the terminal level, that is, on the energy gap. This behavior is interpreted as being due to the simple convergence of the orbit-lattice perturbation expansion. With the precise features of the interacting phonon modes and atomic levels averaged out for these high-order processes, the only critical parameter within a given lattice is the energy gap, ie, the order of the process. The dependence on the order has been extracted by normalizing the energy gap by the optical-phonon cutoff energy. The rate for a given order and the swiftness of the convergence reflect the strength of the orbit-lattice interaction. The relative behavior for a given host can be explained through its known crystalline properties, in particular the phonon frequency distribution function and the static crystal field. The observed order dependence in Y 2 O 3 indicates a relative weakness in the orbit-lattice interaction for crystals with strong covalency.