Spectral tuning of UV luminescence of upconverting nanoparticles (UNPs) enables development of modern applications of upconversion such as infrared-driven photochemistry. We investigated spectral tuning of luminescence of upconverting nanoparticles composed of NaYF4: Yb3+, Tm3+ (69.5:30:0.5). We demonstrated spectral control of luminescence of these UNPs by adding lanthanide ion that acts as a quenching agent for selected wavelengths of luminescence of Tm3+. Erbium (Er3+), which contains an energy level closely matching that of the ultra-violet (UV) energy level of Tm3+ (1D2), was selected as the quenching ion in this study. First, we demonstrated energy transfer between the luminescent ion (Tm3+) and the quenching ion (Er 3+). Subsequently, we demonstrated tuning of the UV luminescence intensity of these UNPs. The desired spectral output of the UNP is dependent on two factors, the selection of the quenching agent and its doping ratio in UNP composition.