Radio-photoluminescence properties of LiCaAlF6:Sm

In this paper, we report radio-photoluminescence (RPL) properties of Sm-doped LiCaAlF6 as a new RPL material. The material was successfully synthesized via the mechanochemical route by mixing LiF, CaF2, AlF3, and SmF3 raw powders in a planetary ball-mill. The resulting powder sample shows photoluminescence (PL) predominantly due to the 4f-4f transitions of Sm3+, indicating that the doped Sm ion is optically activated. After irradiating with X-rays, additional PL emissions appeared around 700 nm; that is, Sm-doped LiCaAlF6 exhibits RPL properties. From the spectral features and luminescence dynamics, the origin of the RPL centre is determined to be the 4f-4f transitions of Sm2+. Therefore, in this material system, intra-valence change of Sm ion (Sm3+ → Sm2+) is induced by X-ray irradiation. Furthermore, using an elementary detector and the RPL signal, we could detect signals under a dose as low as 100 mGy, and the RPL signal is reasonably stable (~2%) under UV excitation over 5 min. The latter stability is attributed to the thermal activation of trapped electrons. In addition, X-ray imaging is demonstrated by utilizing the RPL of LiCaAlF6:Sm as an imaging plate.