Quenching of cathodoluminescence at the centre of hardness indentations on a (100) face of MgO

The behaviour of cathodoluminescence (CL) associated with hardness indents in MgO has been examined. Experiments using conical indenters of different included angles show that the luminescence from the deformed zone at the tip of the indenter is quenched by indentations with a representative strain in excess of a critical value, between 5 and 8%. Electron microscopy of the corresponding deformed structure reveals that although the deformed zone is crystalline, it contains a very high dislocation density in the form of a network of loops. This accounts for the characteristic appearance of CL in the neighbourhood of hardness indents, wear tracks, and other regions of localized contact damage.