The role of FA:K+ and FA:Na+ defects in laser light generation and color image formation at the (100) and (110) surface sites of AgCl and AgBr.

2004 ◽  
Vol 6 (3) ◽  
pp. 626 ◽  
Author(s):  
A. S. Shalabi ◽  
I. A. Z. Al-Ansari ◽  
K. Kh. Al-Naimi ◽  
M. A. Kamel ◽  
A. M. El-Mahdy ◽  
...  
Keyword(s):  
Laser Light ◽  
Color Image ◽  
Image Formation ◽  
Surface Sites ◽  
Light Generation

THE ROLE OF OXIDATION STATES IN LASER LIGHT GENERATION AND COLOR IMAGE FORMATION (II) AN AB INITIO STUDY OF FA: Hg+ AND FA: Hg++ COLOR CENTERS AT THE LOW COORDINATION (100) AND (110) SURFACES OF AgBr CRYSTAL

2005 ◽  
Vol 04 (03) ◽  
pp. 883-905
Author(s):  
A. S. SHALABI ◽  
Kh. M. EID
Keyword(s):  
Ab Initio ◽  
Coordination Number ◽  
Excited States ◽  
Oxidation State ◽  
Laser Light ◽  
Color Image ◽  
Image Formation ◽  
Oxidation States ◽  
Color Centers ◽  
Light Generation

The oxidation states of mercury in F A : Hg+ and F A : Hg++ color centers at the low coordination (100) and (110) surfaces of AgBr play important roles in laser light generation and color image formation. Two simultaneous potentials at these surfaces were 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 F A – defect site 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 mercury, 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 and optical–optical conversion efficiency. All relaxed excited states of the defect-containing surfaces were deep below the lower edges of the conduction bands of the ground state defect-free surfaces, suggesting that the F A : Hg+ and F A : Hg++ centers are suitable laser defects. The dependence of the orientational destruction, recording sensitivity and exciton (energy) transfer on the oxidation state of mercury and the coordination number of the surface ion on 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 Hg++ surfaces of AgBr are significantly more sensitive than the corresponding surfaces. On the basis of quasi Fermi levels, the difference in the sensitizing capabilities between the examined dyes in the excited states is determined.

The role of F A1:Ag+ defects in laser light generation and coadsorption of CO and halogen atoms at the KCl and KBr surface sites. First principles calculations

Open Physics ◽  
2007 ◽  
Vol 5 (4) ◽  
Author(s):  
Safaa Abdelrazik ◽  
Ahmed Shalabi
Keyword(s):  
Halogen Atom ◽  
Laser Light ◽  
Optical Transition ◽  
Tunable Laser ◽  
Anion Vacancy ◽  
Basis Set ◽  
Substrate Interactions ◽  
Surface Sites ◽  
Light Generation ◽  
Conversion Efficiencies

AbstractFA1:Ag+ color center at the low coordination (100) and (110) surface sites of KCl and KBr thin films play an important role in providing tunable laser oscillation and adsorbatesubstrate interactions. Double-well potentials at this site are investigated using ab initio molecular electronic structure calculations. The calculated Stokes shifted (optical transition bands), opticaloptical conversion efficiencies, the probability of orientational destruction, exciton (energy) transfer and Glasner-Tompkins empirical rule suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, and (iii) the choice of the basis set centered on the anion vacancy. The adsorbate-substrate interactions were found to be dependent on the electronegativity of the adatom and on the lattice anion. Optimised geometries and the coadsorption of CO and (F, Cl, Br, I) on KCl and KBr (100) crystals are presented. Calculated chemisorption energies for CO on the (halogen atom/defect free sites of KCl and KBr (100) crystals) showed that the coadsorption of halogen atom tends to block other adsorbate-substrate interactions at the nearest neighbour sites. Thus if halogen atom coverage increases, the CO prefers to be adsorbed on the K+ site of the KCl and KBr (100) surfaces and on KBr relative to KCl.

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