Optical properties of atomic gallium and indium centres in KCl

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Abstract
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 Ga0(1) and In0(1) centres, the analogues of the laser-active Tl0(1) centres, could be identified. Ga0(1) centres have absorption bands peaking at 930, 890 and 620 nm and In0(1) centres at 965, 860 and 610 nm. Up to 2.7 mu m no emission was found for Ga0(1) centres, whereas upon excitation at 965 nm In0(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 Ga0(1), In0(1) and Tl0(1) centres is discussed.