A theoretical consideration is made of the thermal broadening and shift of the impurity energy levels in crystals doped with TR3+ ions using the Hamiltonian of electron-phonon interaction containing linear terms in the lattice variables. I n the method developed for the calculation of these effects the real phonon density distribution is used for the host crystal. The information about this distribution is obtained from the spectrum of vibrational satellites of zero-phonon lines. The calculations are carried out for the thermal broadening and the shift of some lines in the 4F3/2 + 411112 luminescence band of the Nd3+ ion in an YAlO, host crystal.l) The same model was used in [7] for calculations of the parameters of the theory [l] for the R-lines of ruby.

No abstract

The possibib ity of the existence of cleavage in a-A120, single crystals has been estimated by elementary structural considerations and has been shown that the { 1011) and { 1120) planes are the more probable cleavage planes. The values of the fracture surface energy measured by WIEDEEHORN and the estimates of the surface energy made by HABTYAN confirm this conclusion. In crystals with small numbers of blocks and dislocations and low residual stress we really found a perfect cleavage along the { 1011) and { 1120) planes. Therefore the existence of the cleavage is defined by the crystal imperfection. It has been shown in what way the orientation of crystals can be visually determined from the direction of cleavage steps.Ha OCHOBe 3JleMeHTapHbIX CTPYKTYPHbIX PaCCMOTpeHHfi 6~n a OUeHeHa B03-MOmHOCTb Cy4eCTBOBaHHH CnafiHOCTH B KpHCTaJlJlaX Ci-A&os H 6~n o nOKa3aH0, 'ITO ~au6onee aeposmo nomneme cnafiHocTu no ~JIOCKOCTIIM