Visualization of stress distribution has been realized by a nondestructive mechanoluminescence (ML) from ${\mathrm{SrAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}\mathrm{:Eu},$ which can emit three magnitudes higher visible light than that of well-known ML substance of quartz. A simulation result confirms that such a ML image successfully reflects the stress distribution. A kinetic model for ML of ${\mathrm{SrAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}\mathrm{:Eu}$ is proposed.

The idea and successful practice of a stress sensor to sense mechanical stress by an artificial skin, i.e., self-diagnosis thin film, has been realized, through the fabrication of a high-luminescence thin piezoelectric film which can reproducibly emit strong visible light upon stressing. The strongest luminescent film consists of nanosized crystallites of ZnS doped with 1.5 at. % Mn, in which Mn acts as the emitting center. The intensity of the emitted luminescence responds to stress applied directly onto the film or to the underlying material reversibly and reproducibly, so it can be used as an artificial skin to sense mechanical stress.