أعضاء هيئة التدريس - جامعة بنها
The role of oxidation states in laser light generation, color image formation and adsorbate–substrate interactions. Comparative study of FA:Tl+1, FB:Tl+1, FA:Tl+3 and FB:Tl+3 color centers at the (100) and (110) surfaces of AgBr crystal
Computational Materials Science 38 (2006) 144–157 • 2006
معلومات البحث
المؤلفون
A.S. Shalabi a,*, S. Abdel Aal a, W.S. Abdel Halim
الكلمات المفتاحية
Not Available
المجلة العلمية
Computational Materials Science 38 (2006) 144–157
الناشر
Not Available
المجلد
Not Available
العدد
Not Available
الصفحات
Not Available
publication.type
International
رابط البحث
Not Available
المواد المرفقة
Not Available
الملخص
The oxidation states of thallium in FA and FB color centers at the low coordination (100) and (110) surfaces of AgBr play important
roles in laser light generation, color image formation, and adsorbate–substrate interactions. The color center potentials at these surfaces
are investigated by using quantum mechanical ab initio methods. Quantum clusters of variable sizes were embedded in the simulated
Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that were the nearest neighbors to the FA
and FB defect sites were allowed to relax to equilibrium. The calculated Stokes shifts suggest that laser light generation is sensitive to
the simultaneous effects of the oxidation state of thallium, the coordination number of the surface ion, and the choice of the basis set
centered on the anion vacancy. An attempt has been made to explain these effects in terms of Madelung potential, electron affinity,
optical–optical conversion efficiency, and adsorbate–substrate electrostatic potentials.
All relaxed excited states of the defect containing surfaces were deep below the lower edges of the conduction bands of the groundstate
defect-free surfaces, suggesting that the title color centers are suitable laser defects. The dependence of the orientational destruction,
recording sensitivity and exciton (energy) transfer on the oxidation state of thallium and the coordination number of the surface ion is
clarified. The Glasner–Tompkins empirical rule is generalized to include the oxidation state of the impurity cation and the coordination
number of the surface ion. As far as color image formation is concerned, the supersensitizer was found to increase the sensitizing capabilities
of two primary dyes in the excited states by increasing the relative yield of quantum efficiency. The Tl+3 surfaces of AgBr are
significantly more sensitive than the corresponding Tl+1 surfaces. On the basis of quasi Fermi levels, the difference in the sensitizing capabilites
between the examined dyes in the excited states is determined. The adsorbate–substrate interactions were found to be dependent
on the oxidation state of the impurity cation and on the electronegativity of the adatom.
roles in laser light generation, color image formation, and adsorbate–substrate interactions. The color center potentials at these surfaces
are investigated by using quantum mechanical ab initio methods. Quantum clusters of variable sizes were embedded in the simulated
Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that were the nearest neighbors to the FA
and FB defect sites were allowed to relax to equilibrium. The calculated Stokes shifts suggest that laser light generation is sensitive to
the simultaneous effects of the oxidation state of thallium, the coordination number of the surface ion, and the choice of the basis set
centered on the anion vacancy. An attempt has been made to explain these effects in terms of Madelung potential, electron affinity,
optical–optical conversion efficiency, and adsorbate–substrate electrostatic potentials.
All relaxed excited states of the defect containing surfaces were deep below the lower edges of the conduction bands of the groundstate
defect-free surfaces, suggesting that the title color centers are suitable laser defects. The dependence of the orientational destruction,
recording sensitivity and exciton (energy) transfer on the oxidation state of thallium and the coordination number of the surface ion is
clarified. The Glasner–Tompkins empirical rule is generalized to include the oxidation state of the impurity cation and the coordination
number of the surface ion. As far as color image formation is concerned, the supersensitizer was found to increase the sensitizing capabilities
of two primary dyes in the excited states by increasing the relative yield of quantum efficiency. The Tl+3 surfaces of AgBr are
significantly more sensitive than the corresponding Tl+1 surfaces. On the basis of quasi Fermi levels, the difference in the sensitizing capabilites
between the examined dyes in the excited states is determined. The adsorbate–substrate interactions were found to be dependent
on the oxidation state of the impurity cation and on the electronegativity of the adatom.