Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 6, 1015, Lausanne, Switzerland.
Institute for Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020, Vienna, Austria.
Sci Rep. 2023 Mar 8;13(1):3897. doi: 10.1038/s41598-023-31045-5.
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].
我们已经生长出[化学式：见正文]Th:CaF[化学式：见正文]和[化学式：见正文]Th:CaF[化学式：见正文]单晶，用于研究[化学式：见正文]Th 的 VUV 激光可及的第一个核激发态，旨在构建固态核钟。为了达到高掺杂浓度，尽管[化学式：见正文]Th 的极度稀缺（和放射性），我们将晶体体积缩小到与已建立的商业或科学生长过程相比的 100 倍。我们使用垂直梯度冷冻法在 3.2mm 直径的种子单晶上生长，单晶上有一个 2mm 的钻孔口袋，填充有共沉淀的 CaF[化学式：见正文]：ThF[化学式：见正文]：PbF[化学式：见正文]粉末，以生长单晶。已经实现了[化学式：见正文]cm[化学式：见正文]的[化学式：见正文]浓度，具有良好的（>10%）VUV 透过率。然而，[化学式：见正文]Th 的固有放射性在生长过程中驱动放射性诱导的离解，并在凝固后导致辐射损伤。这两者都导致 VUV 透过率下降，目前限制[化学式：见正文]Th 浓度至[化学式：见正文]cm[化学式：见正文]。
