The ability to control ultraviolet (UV) luminescence intensity in a switch-like manner is demonstrated through the use of 980 nm excitation pulse-width modulation in NaYF4:Yb3+,Tm3+ upconversion nanoparticles (UNPs). Varying the ytterbium doping resulted in a single order of magnitude improvement of UV luminescence intensity. The excitation pulse-width modulation technique applied to these optimized UNPs enables 3 orders of magnitude control over UV luminescence intensity while maintaining NIR luminescence emission at 800 nm. Controlled in the switch-like manner, these UNPs can transfer their UV energy to 9,10-diphenylanthracene (DPA). Independent control of NIR luminescence and UV energy transfer through NIR excitation modulation may find applications in the development of multifunctional theranostic systems.