Greetings,
I am a biologist and biomemetic researcher who is interested in the antimicrobial properties of natural ultraviolet radiation. I am aware that most of the devices that employ UV to disrupt microbes use UV-C. Unfortunately, UV-C emitted from the sun is absorbed in the atmosphere before reaching earth.
My question is it possible to change the wavelengths of UV-A and/or UV-B to resemble UV-C?
The problem is that the ratio of the energy of photons in the UV-C domain to the energy of UV-A photons is in the range 2 to 4. In order to get a UV-C photon, at least two UV-A or UV-B photons have to be combined. In principle, illuminating a material with UV-C luminescence by UV-A/UV-B will generate some UV-C radiation but I'm afraid the efficiency will be quite low (a few percent, perhaps). Additionally, I seem to remember that the properties of many UV-C luminescent materials deteriorate fast by aging.
I guess a more efficient way to turn terrestrial sunlight into UV-C would consist of solar cells driving a UV-C lamp (probably via a voltage converter).
The Wien displacement law expresses an inverse proportionality between the absolute temperature T and the wavelength Lmax for which the maximum emission from the lamp for which it was designed is obtained.
Lmax = C / T
Where C is a universal constant whose value is 0.2898 cm.K.
If you use an A or B UV lamp, the only alternative you have is to significantly increase the voltage of your lamp to increase the temperature of the incandescent filament and force it to emit UV radiation at a higher frequency (or lower L), but the filament ( or other) of your lamp will sublimate long before reaching the optimal temperature to emit the UV C radiation. Put simply, you can use an instrument that emits the desired UV C rays but cannot force the laws of physics. If you want UV from the sun, on earth you can only use a lamp that mimics your UV rays, otherwise you have to go to the space above the atmosphere.
Why are you addressing it as unfortunate? Do you want UV exposure?
The UV radiation induces DNA damage through thimidine dimerization. It can be happened to human DNA too.
I can't answer your question, but I can make more questions (in case you do not know about it). Solar research has found through NASA missions like the Solar Dynamics Observatory (SDO) in the EvE subsystem for ultra violet radiation study that UV in extremis (Extreme Ultra Violet [EvE]) radiation has 100 separate emitta. What this does to UV-A/B etc. I do not know. It COULD (could as in maybe) go way past earlier understandings of UV. The EvE subsystem's mission commander was / is (?) Thomas Wood of the High Altitude Observatory (HAO) in Colorado. They're trying to study wavelengths in EvE from source to earth subsurface and its effects (?) Regarding newer research here, and findings, per your kind of research, I'd try to contact the HAO regarding this. Of course, YOU might be in a better position to tell THEM what-is-what.