Protective oxide films, such as alumina, generally luminescence when excited with a laser of an appropriate wavelength. Examples of the use of this luminescence to monitor residual stresses in alumina scales, to establish the conditions for spallation failure and to determine the stress distribution around spalls, holes and free edges are described. To illustrate the potential for extending luminescence to the evaluation of non-destructive evaluation of coatings, an in-situ luminescence sensor is described.