No abstract

Studies of photoinductive dichroism allow to define the orientation of colour centres. The photoinductive dichroism of absorption testifies the fact that oscillators, responsible for the long-wave absorption band of M þ A -centres, are located along h100i crystallographic directions, and high-energetic oscillators, along h110i crystallographic directions. Various impurities cause unequal perturbations in the crystal lattice. The determination of the kinetic parameters of the reorientation processes in simple and complex colour centres allows establishing the structure of the aggregative centre. The size of the impurity ion influences the energy of reorientation of M þ A -centres, and this, in turn, is connected with the displacement of vacancies towards the anion sites of the crystal. It is found that the anion vacancy in M þ A -centres jumps in h110i directions, but in F þ A -centres it jumps in h100i directions. Z. P. Chornyi et al.: Reorientation of M þ A -Centres in CaF 2 : Me + Crystals

The effect of Bi impurity on the optical absorption and roentgeno-, photo-, and thermoluminescence spectra of CdI 2 crystals grown by the Bridgman-Stockbarger method is studied. CdI 2 activation with BiI 3 produces a number of absorption bands related to electronic transitions of Bi 3+ . Bi produces no emission centers in CdI 2 . The 550-to 560-nm luminescence of CdI 2 is due to the radiative recombination of self-trapped anion excitons. The observed changes in spectral distribution and the reduction in light yield upon CdI 2 activation with Bi 3+ are mainly due to the reabsorption of emission from native centers by activator centers. Under x-ray excitation, CdI 2 :Bi 3+ accumulates a small light sum at shallow trap levels related to native defects.

No abstract

The luminescent properties of Mn-activated CdCl 2 , CdBr 2 , CdI 2 , and CaI 2 crystals are studied in the range 4.2-200 K. The photo-and roentgenoluminescence spectra of the crystals show red emission bands due to the Mn activator. The excitation spectra and Mn luminescence kinetics are interpreted in terms of the crystal-field theory with consideration for electron paramagnetic resonance data. The red luminescence of the crystals at 4.2 K is attributed to the 4 T 1 g ( 4 G ) 6 A 1 g ( 6 S ) electron-phonon transitions of Mn 2+ . The Racah parameters B and C are determined. The origin of the 600-nm luminescence in CdBr 2 :Mn 2+ under excitation with a nitrogen laser and xenon lamp at 320-360 nm in the range 4.2-90 K is discussed.