Influence of the anion on the spectroscopy and scintillation mechanism in pure andCe3+-dopedK2

Abstract

The optical properties and scintillation mechanism in pure and Ce 3ϩ -doped K 2 LaX 5 and LaX 3 have been determined under x-ray, ␥-ray, vacuum ultraviolet light, and synchrotron radiation excitation. Special attention is paid to the influence of anions XϭCl Ϫ , Br Ϫ , and I Ϫ , and a comparison is made with properties of pure and Eu 2ϩ -doped KX compounds. The energies of the 5d excited states of Ce 3ϩ have been determined, and the total crystal field splitting and the centroid shift are discussed. An excitation across the band gap creates a combination of self-trapped exciton ͑STE͒ and Ce 3ϩ emission. These emissions are often anticorrelated when temperature or Ce 3ϩ concentration is changed. Their ratio is related to the STE mobility and STE creation rate. Clear trends in the optical properties and scintillation mechanism are observed along the halide series.

First principle quantum description of the energetics associated with LaBr<inf>3</inf>, LaCl<inf>3</inf>, and Ce doped scintillators

“…However, Reaction (5) is much more energetic (671.5 kJ vs. 60.71 kJ) than (6). X-ray excited luminescence for pure LaBr 3 at 100K has two bands near 340 and 430 nm that are attributed to STE luminescence [3]. Similar bands are also observed for pure LaCl 3 [29].…”

“…1. displays the Density-ofStates (DoS) representation for the pure crystal of LaBr 3 . An orbital analysis of this representation is also provided and supports a conclusion that the valence band in the crystal is primarily composed of Br s and p orbitals.…”

“…A similar set of reactions may also be developed for LaCl 3 . For simplicity only LaBr will be discussed.…”

“…To achieve this objective, a variety of computational approaches were needed. A qualitative description of the band gap and atomic orbital contribution to the band gap structure was needed for pure LaBr 3 and LaCl 3 and Ce doped crystal material and was obtained using a plane wave density functional theory (DFT) approach employed in the CASTEP [16]code. La, Br, and Cl were represented by ultra-soft pseudo potentials arranged in a muffin tin arrangement.…”

“…Introduction ver the last seven to eight years, considerable attention was given to the characterization of the photophysical properties of cerium doped lanthanum halides (Cl, Br) that were shown to be outstanding scintillators. Spectroscopic measurements were performed to characterize the scintillation properties of both cerium doped lanthanum chloride and bromide [1]- [3]. These studies revealed that the photophysics of cerium scintillation was dependent on cerium concentration, halogen, and crystal temperature.…”