A persistent spectral hole-burning technique was used to investigate the effect of a uniaxial stress upon the defects which were created by the irradiation of natural Ia-type crystals. Shifts of the spectral holes in the 649, 681, and 774nm zero-phonon lines were determined. The magnitudes of the shifts (2.2, 1.2, 0.65/cm-kbar) which were deduced from these measurements were compared with stress shifts for the lines of defects with a well-known structure. It was suggested that vacancies were present in the defect that was responsible for the 681nm zero-phonon line. A combination of the results, of polarized luminescence and uniaxial stress experiments, led to the conclusion that the defects that gave rise to the 649 and 681nm zero-phonon lines had rhombic I symmetry.

A.Osvet, V.Palm, I.Sildos: Journal of Applied Physics, 1996, 79[11], 8290-3