Relaxation processes in irradiated rubies

Using a dynamic Jahn-Teller model, it is found that the Cr 2+ ion, produced in ruby crystals by x-irradiation, behaves as a fast relaxing impurity with a relaxation time of the order of 10 -9 s at very low temperatures. The problem of cross-relaxation between a Cr 3+ ion and a Cr 2+ ion in the presence of a magnetic field directed along the c axis is analysed in detail by computer using a dipole-dipole interaction Hamiltonian. The associated relaxation time T x is found to be much shorter than the usual Cr 3+ -lattice relaxation time. T x is found to vary with temperature T according to the relation T x α T -n where n is approximately 3·5 in agreement with the measurements of Mason and Thorpe. Possible relaxation processes in irradiated rubies are also briefly examined.