Simon Stellmer and co-workers have published a long paper that summarizes a whole series of experiments performed within the last year. The studies are concerned with the detailed characterization of the photoluminescence, radioluminescence, and thermoluminescence properties of Th-doped CaF2 crystals. Such crystals will be used as a platform for direct optical spectroscopy of the isomer transition. There are, however, considerable worries that the glowing of the crystal itself, as it is subjected to radioactivity and strong UV light, might be much stronger than the faint sought-after nuclear signal. The studies show that the worries are indeed justified, as the crystals emit characteristic luminescence in the UV range. Luckily, the emission wavelength is sufficiently far away from the expected nuclear transition, such that a great deal of crystal luminescence can be filtered away spectrally. The researchers also characterized the decay time of the luminescence and its dependence on temperature. The findings allowed them to develop strategies to further reduce the luminescence background. All in all, this experimental work proofs that CaF2 crystals are a viable platform for optical spectroscopy. The paper is available on the arXiv and has been published with Nature Scientific Reports.