It is noteworthy that the fluorescence characters of the thorium

However, from 210 K, the trend was reversed, where the peak intensity is increased as the increase of temperature. Such phenomenon is associated with a blue shift into the UV region. Compound 2 present a similar phenomenon. From 77 K to 180 K, the peak intensity dropped constantly, while from 210 K to 300 K, the peak intensity gradually increased. Such a reversed correlation between the intensity of the absorption peaks and temperature is likely originated from temperature induced structural changes.
Fluorescence spectroscopy