Similar to how a prism may be used to separate visible light into its individual colors, is there any surface or material that will separate ultraviolet light into the three types of UV light: UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm)?
Or, is there any way to convert between different UV types? For example, can I use a lens and make UV-A enter, and make UV-B exit?
First, you would need a material that is transparent to UV light such as fluorite as conventional glasses are too absorbent. Bear in mind that if you made a prism of such a material then the resulting spectra will be a continuum rather than quantised into these discrete ranges, just as visible light separates into a continuous spectrum through a prism and does not emerge as discrete bands.
I do not think there is any way of converting e.g. UV-A into UV-B. Although the wavelength depends on the medium, the frequency is constant. Short of finding some way to modulate the frequency the UV-A will remain UV-A.
Converting light colors is not always particularly easy, but you can sometimes find the right fluorescent material for the job of downconversion. For example, I happen to know that gallium oxide (Ga$_2$O$_3$) absorbs light with wavelength below 260 nm (UV-C) and then re-emits much of the energy around 360 nm (UV-A).
It is much easier to separate colors you already have. You can purchase dichroic beamsplitters which transmit a certain color range and reflect another. So it would be easy to find a set of two filters, the first of which would reflect the UV-C (transmitting UV-B and UV-A), and the second of which would reflect UV-B (transmitting UV-A).
Prisms made of an appropriate UV-transmissive material will also work fine, but they are a little less practical if you want to work with broad bands of color since the outgoing light will be diverging.
