Two Colour Glow-in-the-Dark Laser Writing
Experimenting with green and red phosphorescent (glow-in-the-dark) paints and a violet/uv laser pointer.
Green glow-in-the-dark canvas with UV/violet laser
A while back I created a glow-in-the-dark canvas using a green strontium aluminate-based (SrAl) phosphorescent paint. This type of paint glows a lot brighter and longer than the older, conventional zinc sulfide-based (ZnS) pgiments. I only had a 30ml bottle so diluted this acrylic-based paint with PVA glue and painted it on a cheap stretched canvas, although anything would do.
The phosphorescent paint can be charged with light with a wavelength in the range 200-450nm. This means any torch or blue and UV LEDs can be used to draw on the canvas. UV LEDs work best as they are least bright on the eye when used in the dark. The cavas is covered with a transparent pastic sheet to protect it from LEDs being brushed against it.
I have wanted to use a laser to draw on the canvas for some time but the only ones available at the time were adapted Blu-ray lasers which came at great expense and were not particularly child friendly. However, recently violet/UV laser pointers (<1mw) have become very affordable (~£8). At 405nm these will excite all phosphorescent paints.
Red glow-in-the-dark paint and Green lasers?
A post had suggested that red ZnS-based paint could be charged with a green laser. I bought some red Zinc Sulfide glow paint and borrowed a green laser to test this out. Unfortunately, my tests proved negative; the green laser did not charge the red paint. This results appears to be backed up by other research that says that the red luminescense of ZnS single crystals is excited by light having a maximum wavelength at 344 or 448nm. Green lasers have a wavelength of 532nm. There appear to be some blue lasers with a wavelength of 450nm - it may be possible that these could excite red ZnS paint.
Two-colour glow in the dark canvas
I have painted over the green canvas with 60ml of the red ZnS paint that I had bought to test with a green laser. The red ZnS paint is 'old-school' glow-in-the-dark paint so is dimmer and fades faster. The result is in the video - some streaks of the canvas glow with an orange that fade to green. Interesting.
The next step is to test this with a blue 450nm laser to see if I can excite only the red paint leaving the green untouched. This would allow a green scene to be created and then red components to be added afterwards. We'll see...
Something else to try is many different coloured SrAl glow paints.