We report on Lu₂(WO₄)₃: Yb³⁺, Tm³⁺ upconversion nanoparticles prepared via modified Pechini method, which is low-cost in comparison with analogs and allows achieving the homogenous rare earth ions (Yb³⁺ and Tm³⁺) dispersion in the host matrix. The Tm³⁺ doping concentration effect on structural and luminescence properties has been studied in detail. The structure of the nanoparticles was characterized by XRD and Raman spectroscopy. Both analytical methods confirmed the formation of single phase Lu₂(WO₄)₃: Yb³⁺, Tm³⁺ nanoparticles without any impurities. It was found that thulium ions are uniformly incorporated into the tungstate structure up to a concentration of 1%. SEM images showed that prepared samples consisted of weakly agglomerated nanoparticles with an average size of about 40–80 nm. Emission and excitation spectra of all Lu₂(WO₄)₃: xTm³⁺, 10% Yb³⁺ samples contained characteristic transitions inside Tm³⁺ ions. Upconversion spectra demonstrated intense infrared line (³H₄–³H₆) as well as weak blue ¹G₄–³H₆ and two red (¹G₄–³F₄, ³F_2,3–³F₆) bands obtained upon 974 nm excitation. Optimal Tm³⁺ doping concentration was found to be 0.3% for both ³H₄–³H₆ and ¹G₄–³F₄ transitions. Change of chromaticity coordinates along with Tm³⁺ amount increase was also observed.