The nature of luminescence of KI and KI-Na crystals at low temperature deformation after natural decrease in the symmetry of the lattice

Abstract

The X-ray luminescence spectra at low temperature (90K) uniaxial deformation were researched for KI and KI-Na crystals, that were stored for more than 10 years. The following regularities were observed: firstly, the intensities of the intrinsic emission bands at 3.3 eV ( π ) and 4.1 eV ( σ ) become equal in comparison with freshly grown crystals; and secondly, with an increase in the degree of low-temperature uniaxial deformation, a gradual shift of the emission spectra occurs in two directions: the luminescence maximum at 3.3 eV shifts towards short wavelengths, the final position is fixed at 3.9 eV, which practically merges with σ -luminescence; the radiation maximum at 3.0 eV (Ex-radiation) is shifted toward long wavelengths, the final position which is fixed at 2.8 eV. Thus, low temperature uniaxial deformation leads to the separation of the emission spectra at 3,3 eV( π ) → 3,9 eV and 3.0 eV ( E x ) → 2,8 eV, which are interpreted by the separation of weak → on and weak → strong exciton configurations , respectively.

Exciton-like luminescence of KCl matrix under thermoelastic, local and uniaxial deformation

“…It is known that during long-term operation of scintillation detectors developed on the basis of AHC by doping with cationic impurities (NaI-Tl, CsI-Tl and CsI-Na), their high luminescence quantum yield constantly decreases with time. This effect is associated with the accumulation of impurities and with the transformation of stable aggregates, which reduces the concentration in the lattice of dispersedly distributed single impurity cations, which are centers of luminescence [30]. As a result of the formation of aggregates in KCl-Na crystal, the concentrations of single sodium ions located in the cationic lattice site sharply decrease, which is the main reason for the extinguishing of the luminescence intensity of KCl-Na crystal, regardless of the sodium concentration (Figure 1).…”

The features of deformation-stimulated RbI luminescence

“…The reliably established mechanisms of the manifestation of the intrinsic luminescence of alkali halide crystals (AHCs), which is carried out through a self-trapped exciton state [1][2][3], formed due to the deformation of the crystal lattice, provides the widest opportunities for further investigation of the radiative relaxation of exciton-like structures with a decrease in the lattice symmetry [4][5][6][7].…”

“…Local deformations due to the difference in the sizes of both anionic and cationic homologues [2,5], point vacancy and radiation defects [12][13], as well as uniaxial elastic deformation [6, 11,14] have traditionally been used as reducing the symmetry of the lattice of AHCs.…”