Self-Trapped Excitons in Ionic-Covalent Silver Halide Crystals and Nanostructures: High-Frequency EPR, ESE, ENDOR and ODMR Studies
Self-Trapped Excitons in Ionic-Covalent Silver Halide Crystals and Nanostructures: High-Frequency EPR, ESE, ENDOR and ODMR Studies
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离子共价卤化银晶体和纳米结构中的自陷激子：高频 EPR、ESE、ENDOR 和 ODMR 研究
DOI：
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发表时间：
2010
影响因子：
1
通讯作者：
Jan Schmidt
中科院分区：
文献类型：
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作者：
Pavel G. Baranov;N. G. Romanov;O. Poluektov;Jan Schmidt
卤化银在固态物理学中具有独特的特征，因为它们的性质被认为具有离子键和共价键之间的边界性质。在 AgCl 中，自捕获空穴 (STH) 位于阳离子亚晶格的中心并部分捕获，由于 Jahn-Teller 畸变，在 (AgCl6)4− 络合物内部形成 Ag2+ 离子。 AgCl 中的 STH 可以从导带捕获电子，形成自陷激子 (STE)。综述了通过高频电子顺磁共振、电子自旋回波、电子核双共振 (ENDOR) 和光学检测磁共振 (ODMR) 进行 STE 研究的最新结果。讨论了 AgCl 晶体中 STE 的性质，例如交换耦合、三重态和单重态亚能级的有序性、单重态和三重态的动力学性质以及与 Ag 和 Cl (Br) 核的超精细相互作用。 ENDOR 获得了有关 STE 不成对电子波函数空间分布的直接信息。与浅电子中心和STH的ENDOR研究结果进行比较，得出电子主要包含在玻尔半径为15.1 ± 0.6 Å的类氢1s轨道中，但其中心附近的电子密度反映了空穴的电荷分布。 STE 的孔实际上与孤立的 STH 中心相同。对于嵌入 KCl 晶体基质中的 AgCl 纳米晶体，与块状 AgCl 晶体相比，STE 和 STH 的 g 因子的各向异性显着降低，这可以通过纳米颗粒中 Jahn-Teller 效应的显着抑制来解释。对 KBr 中 AgBr 纳米晶体的 ODMR 研究揭示了空间限制效应，并允许根据 ODMR 光谱的形状估计纳米晶体的尺寸。
Silver halides have unique features in solid state physics because their properties are considered to be of borderline nature between ionic and covalent bonding. In AgCl, the self-trapped hole (STH) is centered and partly trapped in the cationic sublattice, forming an Ag2+ ion inside of a (AgCl6)4− complex as a result of the Jahn–Teller distortion. The STH in AgCl can capture an electron from the conduction band forming the self-trapped exciton (STE). Recent results of a study of STE by means of high-frequency electron paramagnetic resonance, electron spin echo, electron–nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) are reviewed. The properties of the STE in AgCl crystals, such as exchange coupling, the ordering of the triplet and singlet sublevels, the dynamical properties of the singlet and triplet states, and the hyperfine interaction with the Ag and Cl (Br) nuclei are discussed. Direct information about the spatial distribution of the wave function of STE unpaired electrons was obtained by ENDOR. From a comparison with the results of an ENDOR study of the shallow electron center and STH, it is concluded that the electron is mainly contained in a hydrogen-like 1s orbital with a Bohr radius of 15.1 ± 0.6 Å, but near its center the electron density reflects the charge distribution of the hole. The hole of the STE is virtually identical to an isolated STH center. For AgCl nanocrystals embedded into the KCl crystalline matrix, the anisotropy of the g-factor of STE and STH was found to be substantially reduced compared with that of bulk AgCl crystals, which can be explained by a considerable suppression of the Jahn–Teller effect in nanoparticles. A study of ODMR in AgBr nanocrystals in KBr revealed spatial confinement effects and allowed estimating the nanocrystal size from the shape of the ODMR spectra.