DETERMINATION OF THE PIEZOSPECTROSCOPIC COEFFICIENTS FOR CHROMIUM-DOPED SAPPHIRE

The coefficients of the piezospectroscopic tenser for a 0.05 wt% ruby are evaluated by direct measurement of the frequency shift for uniaxia l compression along the three principal crystallographic directions an d for loading in the three principal shear directions, Although the nu merical value of the trace of the tenser is the same as previously rep orted, the piezospectroscopic coefficients along the c and m direction s are slightly different, Contrary to expectation from the rotational symmetry of sapphire about the c axis, the coefficient along the a dir ection was found to be different from that along the m direction, It a lso varies nonlinearly with strain in the a direction, The difference is attributed to the applied stress breaking the rotational symmetry a bout the c axis and is interpreted in terms of the relative motion of the Cr3+ ion with respect to the nearest-neighbor oxygen ions. An addi tional finding is that there is a significant difference in the piezos pectroscepic tenser for the R1 and R2 lines. This will facilitate a mo re complete determination of the stress tenser from fluorescence measu rements than has hitherto been possible.