To investigate the effect of thermal treatment on the optical properties of NPs dispersions more accurately, dehydrated mixed solvents of DMSO-d/CHBr2CHBr2 was applied to disperse the LaF3:Nd nanoparticles (NPs). These solvents contain few quenching groups and possess similar density, solubility and matching refractive index with LaF3:Nd NPs, which depressed the influence of solvents on the luminescent properties of NPs dispersions to the greatest extent. The effect of thermal treatment on the optical performance of the LaF3:Nd NPs dispersions were characterized by the transmittance, fluorescence spectra and lifetime. An influence model of particle size and relative refractive index on the scattering loss of NPs dispersions was established. An enhancement of lifetime by 60.7% and a suppression of transmittance were observed for the dispersions with LaF3:Nd NPs heat-treated at 500 degrees C. This is verified by the results of the scattering loss calculations based on the Mie scatter theory. These results can offer some constructive suggestions to evaluate the luminescence properties of rare-earth doped NPs in the solvents more accurately.