Structure and properties of electronic and hole centers in CsBr from theoretical calculations

Abstract

The electronic structure, geometry, diffusion barriers and optical properties of fundamental defects of CsBr are calculated using hybrid functional DFT and TD-DFT methods. The B3LYP functional with a modified exchange contribution has been used in an embedded cluster scheme to model the structure and spectroscopic properties of the self-trapped triplet exciton, interstitial Br atoms and ions, self-trapped holes and Br vacancies. The calculated migration barriers and positions of maxima of optical absorption bands are in good agreement with experiment, justifying the obtained defect geometries. The off-center triplet exciton luminescence energy is also accurately calculated.

Ab initio simulations on migration paths of interstitial oxygen in corundum

“…A number of theoretical simulations on anion dumbbells were performed earlier on both alkali metal chlorides (fcc NaCl, KCl [16,18,19] and bcc CsBr [20] as well as alkaline-earth metal fluorides (CaF 2 , MgF 2 and SrF 2 ) [21][22][23], where the equilibrium defect configurations, optical properties and possible migration trajectories of interstitial halogen atoms were simulated. Analogous simulation of dumbbells in metal oxides was earlier performed for fcc-MgO bulk only, where migration paths of O i atom were considered along both [1 1 1] and [1 1 0] crystallographic axes [15].…”

A mechanism of Cu work function reduction in CsBr/Cu photocathodes

“…The position of the F-centre energy level in the bulk CsBr has been determined to be 2.0 eV below the conduction band by optical absorption spectroscopy. 41,42 This is much higher than the Cu(100) Fermi level position with respect to vacuum (see Table 1), hence the electron transfer into Cu. The local anions relax towards the vacancy, and cations away from it.…”

“…A recent publication has estimated the barrier to F + -centre migration as 0.3 eV in the bulk of a-CsBr. 42 If we assume a similar barrier here, we would expect vacancies created in the bulk near the interface to diffuse preferentially to the interface. As an F + -centre is positively charged, it should polarize the metal, giving rise to an attractive force.…”

“…At these energies we can expect di-vacancies to move through the lattice, but at a slower rate than H-centre or F + -centre diffusion, which have barriers of approximately 0.05 and 0.3 eV, respectively. 42 In order to examine the behaviour of di-vacancies around the interface, and their effect on the work function, di-vacancies have been placed in three different configurations at the interface; parallel to the interface, and perpendicular to the interface with both the Br and Cs vacancy in the interface layer. The di-vacancy parallel to the interface is of the lowest energy.…”

Computer Simulations of the Band Structure and Density of States of the Linear Chains of NaCl Ions

“…They have many interesting physical properties such as high melting point, strong miscibility, and large band gaps. Due to the fact that in these materials the effective exciton mechanism [1]- [10] of the formation of radiation defects is implemented, they are widely used as radiation detectors, such as scintillators [11]- [15] and a storage phosphors for image plate detectors and optically stimulated dosimeters [16]- [20]. Moreover, alkali halides are used as infrared (IR) optical windows and optoelectronic devices [21], [22].…”