The numerical coefficients linearly relating the effects of stress (including
pressure), temperature, and composition to shifts in the energies of the Cr-related
fluorescence in alumina (Al2O3) are reviewed. The primary focus is the shift of the R1
and R2 “ruby” fluorescence lines under conditions typical for stress determination in
polycrystalline Al2O3. No significant experimental difference in the R1 and R2 responses
is observed for hydrostatic stress (or pressure) conditions (average shift coefficient
of about 7.6 cm−1/GPa), changes in temperature (about 0.140 cm−1/K), or variations in
composition (about 120 cm−1/mass fraction of Cr). There are significant differences in
the R1 and R2 responses for nonhydrostatic stress conditions. In particular, for
uniaxial stress along the a and c directions in the Al2O3 crystal, the R1
piezospectroscopic tensor coefficients (about 3.0 cm−1/GPa and 1.6 GPa cm−1/GPa,
respectively) differ considerably, whereas the R2 coefficients (about 2.6 cm−1/GPa and
2.3 GPa cm−1/GPa, respectively) do not. Measurements of the piezospectroscopic tensor
coefficients are shown to have interlaboratory relative consistency of about 4 %
extending over 30 years, and are consistent with the scalar high-pressure measurements.
Measurements of the temperature coefficients are shown to have interlaboratory relative
consistency less than 1 % extending over 60 years. Fluorescence-based measurements of
stress in polycrystalline Al2O3, although requiring temperature adjustment, are shown to
have a relative uncertainty of about 2.5 %.