Determination of the Piezospectroscopic Coefficients for Chromium‐Doped Sapphire

Abstract

The coefficients of the piezospectroscopic tensor for a 0.05 wt% ruby are evaluated by direct measurement of the frequency shift for uniaxial compression along the three principal crystallographic directions and for loading in the three principal shear directions. Although the numerical value of the trace of the tensor is the same äs previously reported, the piezospectroscopic coefficients along the c and m directions are slightly different. Contrary to expectation from the rotational symmetry of sapphire about the c axis, the coefflcient along the a direction was found to be different from that along the m direction. It also varies nonlinearly with strain in the a direction. The difference is attributed to the applied stress breaking the rotational symmetry about the c axis and is interpreted in terms of the relative motion of the Cr 3+ ion with respect to the nearest‐neighbor oxygen ions. An additional finding is that there is a signiflcant difference in the piezospectroscopic tensor for the Rl and R2 lines. This will facilitate a more complete determination of the stress tensor from fluorescence measurements than has hitherto been possible.