The screen material has a lot to do with what a 405nm diode spot will look like. Some paper has whitening agents in it and if you wash a white sheet in the right kind of detergent it will also. When you shine a 405nm laser on that it looks bright bluish white. You can't see the violet at all. If you are interested in using fluorescent pigments, you will probably find that the blue laser lights it up just as well as the violet.