Photoluminescence Properties of X-Ray Generated Divalent Sm in Mechanochemically Prepared Nanocrystalline CaF₂:Sm3+

Abstract

In this study, the mechanochemical preparation of nanocrystalline CaF2:Sm3+ by ball milling calcium acetate hydrate, samarium (III) acetate hydrate, and ammonium fluoride is reported. The photoluminescence of the as-prepared CaF2:Sm3+ shows predominantly Sm3+ 4G5/2 → 6HJ(J = 5/2, 7/2, 9/2, and 11/2) f-f luminescence, but intense electric dipole allowed 4f55d (T1u) → 4f6 7F1 (T1g) luminescence by Sm2+ was generated upon X-irradiation. In comparison with the co-precipitated CaF2:Sm3+, the conversion of Sm3+→ Sm2+ in the ball-milled sample upon X-irradiation is significantly lower. Importantly, the present results indicate that the crystallite size and X-ray storage phosphor properties of the lanthanide-doped nanocrystalline CaF2 can be modified by adjusting the ball milling time, dopant concentration and post-annealing treatment, yielding crystallite sizes as low as 6 nm under specific experimental conditions.