Optical properties of atomic gallium and indium centres in KCl

In radiation-damaged In- and Ga-doped KCl crystals many In- and Ga-related defects are formed. Their optical absorption bands strongly overlap, making it impossible to determine the optical transitions of a particular defect directly. With measurements of the magnetic circular dichroism tagged by electron spin resonance absorption bands of Ga 0 (1) and In 0 (1) centres, the analogues of the laser-active Tl 0 (1) centres, could be identified. Ga 0 (1) centres have absorption bands peaking at 930, 890 and 620 nm and In 0 (1) centres at 965, 860 and 610 nm. Up to 2.7 mu m no emission was found for Ga 0 (1) centres, whereas upon excitation at 965 nm In 0 (1) centres probably have a very weak emission around 2.2. mu m. In a model calculation the occurrence of radiative and non-radiative transitions upon excitation of the lowest excited state in Ga 0 (1), In 0 (1) and Tl 0 (1) centres is discussed.