We report the synthesis of NaYF 4 nanoparticles doped with rare earth ions Yb 3+ , Tm 3+ , using the solvotermal method. These nanoparticles were synthesized varying the concentration of Tm 3+ , considering 0.5%; 1.0%; 1.5% and 2.0% of Tm 3 + instead of the Y ions in NaYF 4 in order to study variations in their emissions around 480 nm. The results show a better performance of 1% Tm 3+ doped nanoparticles. We report emission spectroscopy results using a 980 nm diode laser.