Fracto-mechanoluminescence from ruby and Cr doped spinel in cutting, grinding and polishing processes

Red colored bright visible light fracto-mechanoluminescence was observed successfully from ruby (Cr doped Al2O3) and Cr doped spinel (Cr doped MgAl2O4) crystals in mechanical processes such as cutting, grinding and polishing. Fracto-mechanoluminescence spectra from ruby (peaking at λ=696 nm) and Cr doped spinel (peaking at λ=693 nm) perfectly agree with those of photoluminescence (PL) from Cr3+ ions in ruby and spinel crystals, respectively. In the grinding and polishing processes, peak intensities and peak wavelength of fract-mechanoluminescence from ruby and Cr doped spinel crystals varies with roughness (grain size, #) of the diamond disk. Fracto-mechanoluminescence is expected to be used in the in-situ evaluation of fracture of crystals in cutting, grinding and polishing for highly precise mechanical processes.