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Growth and characterization of thorium-doped calcium fluoride single crystals.

Authors :: Beeks K
Sikorsky T
Rosecker V
Pressler M
Schaden F
Werban D
Hosseini N
Rudischer L
Schneider F
Berwian P
Friedrich J
Hainz D
Welch J
Sterba JH
Kazakov G
Schumm T
Source :: Scientific reports [Sci Rep] 2023 Mar 08; Vol. 13 (1), pp. 3897. Date of Electronic Publication: 2023 Mar 08.
Publication Year :: 2023
Abstract: We have grown [Formula: see text]Th:CaF[Formula: see text] and [Formula: see text]Th:CaF[Formula: see text] single crystals for investigations on the VUV laser-accessible first nuclear excited state of [Formula: see text]Th, with the aim of building a solid-state nuclear clock. To reach high doping concentrations despite the extreme scarcity (and radioactivity) of [Formula: see text]Th, we have scaled down the crystal volume by a factor 100 compared to established commercial or scientific growth processes. We use the vertical gradient freeze method on 3.2 mm diameter seed single crystals with a 2 mm drilled pocket, filled with a co-precipitated CaF[Formula: see text]:ThF[Formula: see text]:PbF[Formula: see text] powder in order to grow single crystals. Concentrations of [Formula: see text] cm[Formula: see text] have been realized with [Formula: see text]Th with good (> 10%) VUV transmission. However, the intrinsic radioactivity of [Formula: see text]Th drives radio-induced dissociation during growth and radiation damage after solidification. Both lead to a degradation of VUV transmission, currently limiting the [Formula: see text]Th concentration to [Formula: see text] cm[Formula: see text].<br /> (© 2023. The Author(s).)