It would be interesting to replicate this with a shorter wavelength. I tried doing some stuff with UV LEDs but was frustrated by how inefficient they were. Bog standard 385nm "UV" LEDs emit so much blue light that weak fluorescence was easily washed out. I wonder if that could be messing with your calibration (or even if the extra blue light could be doing some sort of quenching).

the COB uv leds are much cleaner UV, in a normally lit room you can barely see the light blob where you aim them until you hit something that fluoresces. Also the lasers are pretty pure, from what i've seen personally.

But anything in the portion of UV that makes ozone doesn't get anywhere near that small - the smallest is about the same volume as a AA battery, just more squat (larger radius), and they require AC voltage, and none of the ones i got lasted very long, i imagine my AC supply didn't have enough current. they use ~18V iirc? maybe 10V, i don't remember. it's low voltage, though.