Deformation-induced enhancement of Ex-emission in RbI and KI single crystals

Drastic changes in the spectra of X-ray luminescence have been detected in pure RbI and KI single crystals exposed to uniaxial elastic deformation at 85 K. The intensity of both the σ-component of self-trapped exciton (STE) emission (maxima at 4.2 and 3.9 eV in RbI and KI, respectively) and the co-called E_x-luminescence (peaked at 3.05 eV in RbI and at 3.1 eV in KI) linearly increases with relative degree of deformation up to ε ≈ 1 %. The similarity of the dependence I = f(ε) for both emissions confirms the intrinsic origin of the E_x-luminescence in KI and RbI. Using a KI:Tl crystal as an example, it has been shown that low-temperature uniaxial elastic deformation causes a reduction in the mean free path of anion excitons, and, in turn, increases the efficiency of their self-trapping at regular lattice sites and subsequent radiative decay of STEs.