Temperature-induced luminescence from uranyl crystals

Crystals of uranyl nitrate hexahydrate emitted flashes of green light when they were cooled by liquid nitrogen and again when they were warmed to room temperature. These flashes were induced by a change in the temperature of the crystal. The intensities of these flashes and the temperatures at which these flashes occurred were recorded with a homemade apparatus. The flashes occurred between 77 K and 150 K. The temperatures associated with the flashes were random during the cooling and warming of the crystal. They also varied from one crystal to the next.;It is hypothesized that the flashes occurred in the crystal of uranyl nitrate hexahydrate were caused by the water of crystallization. This hypothesis is supported by the fact that crystals of cesium uranyl nitrate, which do not have any water of crystallization, did not show any temperature-induced flashes. The role of the water of crystallization in the temperature-induced luminescence is discussed.