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首页> 外文期刊>Physica, B. Condensed Matter >F-2(+) laser activity and photographic sensitization at the low coordinated surfaces of AgBr: ab initio calculations
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F-2(+) laser activity and photographic sensitization at the low coordinated surfaces of AgBr: ab initio calculations

机译：AgBr低配位表面的F-2（+）激光活性和感光性：从头算

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摘要

The two-fold potential of F-2(+) center at the low coordinated surfaces of AgBr thin films in providing tunable laser activity and photographic sensitization is investigated using ab initio methods of molecular electronic structure calculations. The explicitly considered clusters were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. The neighbor ions nearest to the F-2(+) defect sites were allowed to relax to equilibrium in each case. As far as the tunable laser is concerned, F-2(+) laser activity increases significantly as the bromine coordination decreases from 5 (flat) to 4 (edge) to 3 (Br- corner). The smallest calculated Stokes-shift at the flat surface suggests that emission has the same oscillator strength as absorption. All relaxed excited states (RESs) are deep below the conduction bands of the perfect ground state surfaces. More than one band are expected for edge and corner surfaces. The Br- corner of AgBr is the least probable site for RES orientational destruction of F-2(+). The excited state at the corner has higher energy than that at the flat or at the edge surfaces. F-2(+) can be readily formed at the bromine corner relative to the flat and edge surfaces. The Glasner-Tompkins relation is generalized to include the reduced bromine coordination at the surfaces of the AgBr host. As far as photographic sensitization is concerned, while the alternating pattern of s(1) silver atoms in the vapor phase was retained, it was destroyed in the crystal environment. The F-2(+) defect containing surface of AgBr is developable with a minor activation energy barrier to electron transfer from the developer. Defect mobility makes electron transfer from the developer more facile in the process of visible image formation. About 58% of the reduction of silver ions at the flat surface of AgBr are attributed to the host anions and F-2(+) defect formation, leaving ca. 42% for the reduction of photoelectrons and developer molecules. The rotational diffusion of the central Ag-2 by 90degrees increases the last percentage to ca. 60%, but is hindered by an energy barrier of ca. 1.66eV. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 82]
机译：使用分子电子结构计算的从头算方法研究了AgBr薄膜低配位表面上F-2（+）中心的两倍电位，以提供可调节的激光活性和感光性。明确考虑的簇被嵌入到模拟库仑场中，该场库拉近似于宿主表面的马德隆场。在每种情况下，允许最接近F-2（+）缺陷位点的相邻离子松弛至平衡。就可调谐激光器而言，随着溴配位从5（平面）降低到4（边缘）再降低到3（拐角），F-2（+）激光器的活动显着增加。在平坦表面上计算出的最小斯托克斯位移表明，发射具有与吸收相同的振荡器强度。所有松弛的激发态（RES）都在理想基态表面的导带之下。边缘和拐角表面预期会有一个以上的带。 AgBr的Br-角是RES定向破坏F-2（+）的可能性最小的位点。拐角处的激发态比平面或边缘表面的激发态具有更高的能量。 F-2（+）可以很容易地在相对于平面和边缘表面的溴角处形成。广义的Glasner-Tompkins关系包括在AgBr主体表面上减少的溴配位。就照片敏化而言，虽然保留了气相中s（1）银原子的交替模式，但在晶体环境中却被破坏了。含有F-2（+）缺陷的AgBr表面可以通过较小的活化能垒来显影，以防止电子从显影剂转移。缺陷迁移率使得在可视图像形成过程中电子更容易从显影剂转移。 AgBr平面上银离子的还原量中约58％归因于主体阴离子和F-2（+）缺陷的形成，约有。 42％用于还原光电子和显影剂分子。中心Ag-2的旋转扩散90度将最后一个百分比增加到大约。 60％，但受约60的能量屏障的阻碍。 1.66eV。 （C）2002 Elsevier Science B.V.保留所有权利。 [参考：82]

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