GROWTH AND SPECTROSCOPY OF CHROMIUM-DOPED SRXGA3O7 (X = LA, GD) CRYSTALS

Single crystals of chromium doped SrLaGa3O7 and SrGdGa3O7 were grown b y optical zone melting in air and by the Czochralski method in an atmo sphere of nitrogen containing 1% oxygen. Crystals grown in air were bl ue and strongly dichroic, whereas those obtained by the Czochralski me thod contained separate yellow, green and blue regions. The crystal st ructure of these compounds are such that they have only tetrahedral si tes which may be occupied by chromium ions. Therefore it is probable t hat the colour of the crystals is associated mainly with the absorptio n of Cr4+ ions and lattice defects resulting from deviation from stoic hiometry. Annealing of crystals in oxygen has a small influence on the optical absorption of the blue and green regions of the crystals but the yellow regions recover the absorption bands attributed to Cr4+ ion s. No luminescence has been detected down to liquid helium temperature . (C) 1998 Elsevier Science B.V. All rights reserved.