I believe that GITD and fluorescent materials, which are considered in this thread, have their absorption already at 400nm or even 450nm. Otherwise one will not see any fluorescence at all, if the wavelength is "not enough". The transition from ground state to excited state does not need very much energy (or very short wavelength). On the contrary, the thing which matters is a good match between the energy of excitation light quantum and the energy of the transition to upper state in the fluorescent system. By going to deep UV one may be moving away from the optimum wavelength and thus shorter wavelength UV may be even less efficient for charging GITD and fluorescing.
One obvious fact is that deeper UV is harder to see both with eyes and camera. Thus, reemitted light will be more saturated and will not have blue component on the photos, as it is clearly seen on the glowpaints how-to page.