Thanks Bill, Larry and Ron. To Ron's query - the material for the 'screen' must fluoresce and convert near-UV [=CaK] to a longer wavelength like green light that the eye is more sensitive to. A green glass or plastic material will not work unless the pigments within it fluoresce. The domestic fluorescent tube works on the same principle.

Larry - I don't think a fluorescent pen clip [or the body of the pen itself] can be pushed further beyond confirming a principle. I'm continuing to experiment with other suitable materials that fluoresce and will keep those interested duly posted.