I think I might have it? It looks like silicon dioxide shifts what wavelengths it absorbs when hot, so I think it becomes more opaque to the ultraviolet wavelengths uranium fluoresces from.
www.physicsgurus.com/19911/absorp...
physicsgurus.com
How is the absorption spectrum of an element affected by temperature change? - Physicsgurus Q&A
Temperature can affect the absorption spectrum of an element in several ways:
