Wilhelm Conrad Roentgen was experimenting with a Hittorf-Crookes tube that emitted cathode rays and caused certain materials to luminesce. Because he thought their effect might be obscured by the strong luminescence of the tube itself, he carefully covered the tube with pieces of black cardboard.
This technique is based on the observation that some bacteria (e.g., Vibrio fischeri) luminesce in proportion to cellular metabolism; accordingly, toxicity to the microorganisms is detected as a decrease in the intensity of luminescence.
It is tempting to correlate the size and abundance of light sources in the cloud with the epidermal organs of Vampyroteuthis, but we have never seen the latter luminesce.
Luminescence was observed under 254 nm short-wave (SW) and 365 nm long-wave (LW) UV radiation from a 6 W lamp (model UVP UVSL-26P), and also under broadband UV from the GGTL DFI system using the three different excitations that made the sample luminesce distinctly: 250-350 nm (SW/ LW band), 300-410 nm (LW band 1) and 355375 nm (LW band 2).
This prompted us to tackle the problem of one-step synthesis of tridoped CdS and ZnS and their characteristic luminesce for possible exploitation as tagging materials.