NaBiF₄:Yb³⁺/Er³⁺ upconversion nanoparticles were synthesized by a solvothermal method. The effects of reaction temperature and time on the composition, morphology and luminescence properties of NaBiF₄:Yb³⁺/Er³⁺ were investigated. The results show that increasing the reaction temperature and time in the solvothermal reaction properly enhance the crystallinity of NaBiF₄:Yb³⁺/Er³⁺, and improve the upconversion luminescence efficiency. It is easy to produce the bismuth at the temperature of >220 ℃. In addition, the upconversion luminescence intensity of NaBiF₄:Yb³⁺/Er³⁺ can be also enhanced via Rb⁺ ion doping. The green and red emissions of NaBiF₄:Yb³⁺/Er³⁺ doped with 5 mol% Rb⁺ ions increase to 1.73 and 1.5 times, respectively. The temperature sensitivity of the upconversion luminescence was examined. The fluorescence intensity ratio of the samples at 300-500 K was characterized by a fluorescence intensity ratio (I_FIR) technique. It is indicated that the NaBiF₄:Yb³⁺/Er³⁺ samples could have a potential application in the field of temperature sensor.