No abstract

The polarization diagrams of the luminescence at 400 nm of colour centres in YAG crystals have been measured under exatation in absorption bands at 370 and 235 om. The results suggest that the Centre is most likely to be a one-electron centre involving an oxygen vacancy and aperturbingagent in the adjacent Alo,site.

The colour centres introduced in sapphire crystals by neutron irradiation and by thermochemical treatment exhibit polarized luminescence. In neutron-irradiated crystals an absorption band at 4.1 eV and luminescence bands at 2.45 and 3.8 eV are due to one type of centres, most probably interstitial aluminium ions. Other donor-type centres give rise t o an absorption band at 2.75 eV and a luminescence band at 2.2 eV. In magnesium containing crystals similar centres absorbing a t 2.93 eV and emitting a t 2.35 eV can be introduced by thermochemical treatment in reducing atmosphere. The preliminary study of the red luminescence indicates its connection with the absorption bands a t 3. 45

No abstract