Luminescence from Self-Trapped Excitons in KBr: Na

Abstract

Luminescence from KBr containing Na⁺ ions (3×10⁻⁵−9×10⁻² mol fraction) is investigated at 10 K either by exciting crystals with the UV light or the F band light in X-rayed crystals. Emission bands related to Na⁺ ions are identified at 2.72 and 2.90 eV; both of them polarize perpendicular to the V_K type molecular axis. Their decay times obtained with an N₂ laser excitation are 35 and 24 μs, respectively. It is concluded that the Na emission is π-type emission from a self-trapped exciton, (V_K+e)^*, perturbed by Na⁺ ion. Relative intensity of the 2.72 eV band to the 2.90 eV band varies depending upon the excitation energies and the thermal history of X-rayed crystals. This means that at least two types of the V_KA center with different thermal stabilities should be assumed.