FAR ULTRAVIOLET REFLECTANCE SPECTRA AND ELECTRONIC-STRUCTURE OF IONIC-CRYSTALS
FAR ULTRAVIOLET REFLECTANCE SPECTRA AND ELECTRONIC-STRUCTURE OF IONIC-CRYSTALS
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DOI：
10.1103/physrevb.5.662
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发表时间：
1972-01-01
影响因子：
3.7
通讯作者：
RUBLOFF, GW
中科院分区：
文献类型：
--
作者：
RUBLOFF, GW
用同步辐射作为光源，在90 K< T< 400 K，光子能量范围为6 eV<ω< 36 eV的条件下，测量了一些离子晶体的正入射反射光谱。所研究的晶体包括KCl、KBr、RbCl、CsCl、CsBr、CaF2、SrF2和BaF2.光谱进行了比较和分析，特别是参考它们对温度，化学成分和晶体结构的依赖。特别注意的是由电子激发的p核心水平，形成的+离子的外壳的光谱占主导地位的区域。尖锐的峰（宽度≤ 0.2 eV）表征了该区域的较低能量部分。它们与+离子的身份相关，并被分配到布里渊区使用其观察到的温度依赖性和分离的过渡。的证据进行了分析，发现有利于解释这些峰的核心激子。在更高的能量下，出现了更宽的结构（宽度> 0.5 eV），被认为是由芯电子的带间跃迁引起的。由于这里研究的晶体包含三种不同的晶体结构，因此可以将核心带间光谱的形状不仅与晶体结构相关联，而且实际上与+离子的最近邻配位相关联。在升高的温度下晶格振动的价带和导带能量的加宽产生强烈的温度依赖性的带间以及整个光谱区域的激子结构。离子晶体中光学结构的固有清晰度，这使得可以观察到温度展宽，归因于强离子特性和晶体本征态的局部化，因为这些特性产生相当尖锐的带间态密度以及激子。
The use of synchrotron radiation as a light source has made possible the measurement of the normal-incidence reflectance spectra of a number of ionic crystals in the photon energy range 6 eV< ℏ ω< 36 eV for temperatures 90 K< T< 400 K. The crystals investigated include KCl, KBr, RbCl, CsCl, CsBr, Ca F 2, Sr F 2, and Ba F 2. The spectra are compared and analyzed with particular reference to their dependence on temperature, chemical composition, and crystal structure. Special attention is given to the region of the spectra dominated by electronic excitation of the p core levels which form the outer shell of the+ ions. Sharp peaks (width≤ 0.2 eV) characterize the lower-energy portion of this region. They are correlated with the identity of the+ ion and are assigned to transitions in the Brillouin zone using their observed temperature dependence and separation. The evidence is analyzed and found to favor the interpretation of these peaks as core excitons. At higher energies, there appear broader structures (width> 0.5 eV) considered to be caused by interband transitions of core electrons. Because the crystals studied here encompass three different crystal structures, it is possible to correlate the shape of the core interband spectra with not only the crystal structure, but in fact with the nearest-neighbor coordination of the+ ions. The broadening of valence-and conduction-band energies by lattice vibrations at elevated temperatures produces strong temperature dependence of interband as well as excitonic structures throughout the spectral region. The inherent sharpness of the optical structures in ionic crystals, which allows the temperature broadening to be observed, is attributed to the strong ionic character and localization of the crystal eigenstates, because these properties produce fairly sharp interband densities of states as well as excitons.