Low temperature γ-irradiation effect on KCl:Eu(2+) crystals

The formation of color centers at liquid nitrogen temperatures (LNT) (measured after warming to room temperature) in γ-irradiated KCl crystals doped with Eu(2+) ions in a wide concentration range is studied by optical absorption, emission and the ITC method. No effect of post-irradiation warming up to RT on Eu(2+)-dipole concentration is observed. The ITC measurements reveal the drastic decrease of concentration of isolated europium dipoles induced by LNT irradiation. Moreover, the relationship between F center and Eu(2+) dipoles is different than that predicted by the theory. The results obtained are explained by radiation induced aggregation of Eu(2+) dipoles into small clusters at LNT. (author)