Cs Eu Br 3 : Crystal structure and its role in the photostimulation of CsBr:Eu2+

Abstract

Structure and photostimulated luminescent properties of Eu-doped M 2 Ba X 4 ( M = Cs , Rb; X = Br , Cl) CsBr: Eu 2+ has recently been investigated as a photostimulable x-ray storage phosphor with great potential for application in high-resolution image plates. In a recent paper Hackenschmied et al. ͓J. Appl. Phys. 93, 5109 ͑2003͔͒ suggested that segregations of CsEuBr 3 or Cs 4 EuBr 6 formed within CsBr: Eu 2+ during annealing are responsible for an increase in the photostimulated luminescence ͑PSL͒ yield. In this work single crystals of CsEuBr 3 were prepared by a one step synthesis and identified by x-ray diffraction ͑XRD͒ analysis as single phase perovskites. It was concluded that, after preparation, CsEuBr 3 degrades in normal atmosphere into at least two phases, one of which is the orthorhombic structure of Cs 2 EuBr 5 · 10H 2 O. The XRD powder diffraction pattern of this compound is very similar to that of the segregations observed within CsBr: Eu 2+ and reported by Hackenschmied et al. However, the increased PSL yield in CsBr: Eu 2+ after annealing cannot be due to the segregations, because the trivalent nature of the europium in the segregations renders them PSL inactive.

The Emergence of the Mixed Perovskites and Their Applications as Solar Cells

“…It is found that MA and FA are able to stabilize the PVSK, while other cations with similar size, such as CH 3 CH 2 NH 3 + , [29] (CH 3 ) 2 NH 2 + , [30] would form a non-PVSK structure. Compared to their oxide counterparts, the less negative charge and larger ionic size of halides only allows for B site metal cations to be selected from a few elements, including the alkaline earth, [31] bivalent rare earths, [32] and group 14 elements (Pb 2+ , Sn 2+ , Ge 2+ ). [33,34] 6 ] 4− octahedra.…”

The role of hydrogen- and hydroxyl-doping in CsBr:Eu2+

“…These additional peaks could not be identified through the ICDD database. Maybe, they are attributed to the degradation of CsEuBr 3 phases as reported by Hesse et al [6,7]. Fig.…”

“…The hydrogen atoms are located interstitially at the face-centered sites in the bcc CsBr lattice, which is detrimental to the transformation from Eu-Vc s IDC to CsEuBr 3 AC. Hesse et al [6] reported that the emission peaks of Eu 2+ (5d 6 -4f 7 ) are at 440 and 452 nm in CsBr and CsEuBr 3 . Hence, we suppose that the red shift is due to an increasing number of CsEuBr 3 AC.…”

“…Recently, several authors reported an increase in PSL intensity of CsBr:Eu 2+ when it annealed in air or H 2 S. Hesse et al concluded that a special kind of Eu 2+ -O 2À and Eu 2+ -S 2À dumbbells were created as PSL active emission centers during annealing, which were responsible for the strong increase in PSL yield. The oxygen or sulphur impurities seem to be a part of the hole traps [4,6,7].…”

“…The photostimulated luminescence (PSL) mechanisms of CsBr:Eu 2+ have been intensively studied, typically focusing on electron and hole traps [3][4][5][6][7]. According to these mechanisms, F (Br À ) centers are confirmed as electron traps, and the isolate dipole centers Eu 2+ -V Cs (IDC) or the aggregate centers (AC) Cs-Eu-Br system are proposed as hole traps.…”