Radiation effects in pure and doped Al2O3 crystals

Effects of beta-, X- and UV-radiation on optical properties of nominally pure as well as of variously doped alpha-Al2O3 crystals were studied. Optical absorption, thermoluminescence (TL) and photoluminescence (PL) were measured, The irradiation with wavelengths below 145 nm had essentially the same effects as X-irradiation, indicating that the same defects were formed in both cases. F and F+ emission bands at 410 and 330 nm appeared in the TL and in the PL of all samples. In crystals doped with rare-earth ions the narrow bands, characteristic for these impurities, were dominant. In some of the nominally pure samples also a strong Cr3+ band appeared at 698 nm. In the C-doped crystals the TL and PL emissions were relatively strong and dominated by the F and F+ emission bands. These results support previous suggestions regarding a high anion vacancy concentration in the C-doped crystals. A weak emission band appeared near 500 nm with an excitation maximum near 300 nm and is attributed to interstitial Al: ions. Prolonged UV-illumination with F-light caused a notable increase in the PL yield in the C-doped samples, Irradiation into the Al-i(+) absorption band at 300 nm had a reverse effect and was also efficient for the optical bleaching of the phototransferred TL (PTTL). (C) 1998 Elsevier Science B.V. All rights reserved.