Stress dependence of F+-center cathodoluminescence of sapphire

The rate of spectral shift with applied biaxial stress [piezospectroscopic (PS) coefficient] was determined for the electron-stimulated F+ luminescence emitted from the c plane of sapphire (α-Al2O3) as Π=1.18±0.03nm∕GPa. The PS dependence could be determined to a degree of precision by applying a controlled biaxial stress field to a sapphire thin plate using a ball-on-ring biaxial bending jig and by measuring in situ the spectral shift of the emitted cathodoluminescence (CL) F+ band in a field-emission-gun scanning electron microscope. The ball-on-ring PS calibration results open the possibility of applying CL/PS assessments to directly determine unknown residual stress fields in sapphire-based devices using the optical activity of its oxygen vacancies.