Synthesis of Self-glowing Crystals of Zircon and Zirconia Doped with Plutonium-238 and Terbium

Abstract

Durable crystalline actinide host phases of ceramic waste forms are considered as advanced materials which are prospective for safe use of Pu and minor actinides before their final disposal. Development of self-glowing actinide-doped materials with matrices that are chemically inert and resistant to radiation damage may significantly change the approaches to actinide immobilization. Single crystals of zircon doped with different amount of Tb and 238 Pu were synthesized by the flux method. Different non-radioactive crystals of Tb-doped zircon were studied first by cathodoluminescence method in order to identify the optimal content of Tb 3+ that provides the highest luminescence emission. Then self-glowing crystals of zircon were grown with the optimal Tb content and small admixture of 238 Pu (less than 0.1 wt. %). It was proposed that the valence state of Tb incorporated into zircon crystals can be (3+) and (4+), but only trivalent Tb is responsible for intensive luminescence. It is demonstrated that a small addition of Zr-phosphate to the flux supports Tb incorporation into zircon lattice and stabilizes preferably Tb 3+ . At the same time the addition of Zr-phosphate caused the crystallization of zirconia as a minor phase. Zircon crystals with very intensive self-glowing were successfully synthesized. The 238 Pu content was 0.02 wt.% and the Tb concentration varied between 0.2 and 0.3 wt.%. Zirconia crystals obtained from the same experiment are characterized by weak self-glowing, although the Tb content was only 0.02 wt.%, while the content of 238 Pu was comparable to that of zircon, i.e. 0.03 wt. %.