At present, rare-earth ion-doped up-conversion luminescent materials (UCNP) have attracted widespread attention due to their massive potential of practical application in various fields like color display, biological imaging, solar cells, photodynamic therapy, solid-state lasers and more. Among various rare earth elements, Sc is situated at the top of the third main group and at the beginning of the transition element. With the minimum ionic radius, it demonstrates different physical and chemical properties to Y, Gd, and Lu-based materials. Although Na₃ScF₆ is regarded as a new and efficient host material for its consistent chemical properties and low phonon energy, there are still few studies focusing on it. Allowing for this, the solvothermal method was adopted in this study, with oleic acid (OA) and octadecene (ODE) as complexing agents. On the basis of OA:ODE=10 mL:10 mL and NaF:Ln³⁺=4:1, a series of monoclinic Na₃ScF₆:Yb/Er nanocrystals were synthesized at the temperature of 260, 280, and 300 ℃, respectively. The phase, microstructure and upconversion luminescence properties of the samples were characterized by X-ray diffractometer, transmission electron microscope and fluorescence spectrometer, respectively. Research indicates: when the reaction temperature reached 260 ℃, the sample was monoclinic Na₃ScF₆:Yb/Er (PDF No.47-1221) nanospheres with a particle size of about 20 nm; when the reaction temperature reached 300 ℃, the sample was monoclinic phase Na₃ScF₆:Yb/Er (PDF No.20-1221) nanocrystals with a size of about 18 nm, exhibiting high crystallinity and excellent dispersion. Having a mixed phase of PDF No.47-1221 and PDF No.20-1221 at 280 ℃, the sample demonstrated uniform morphology and excellent dispersion, with a particle size of about 30 nm. Under the excitation of a 980 nm laser, the upconverted luminescence color of the sample shifted from red light to green light when the reaction temperature was raised from 260 to 300 ℃, while the luminous intensity showed a significant increase to about 3.1 times the original level. Moreover, a discussion was conducted about the evolution of the sample morphology with time at 300 ℃. This work achieves a controllable output of Na₃ScF₆:Yb/Er nanocrystal upconversion luminescence color only by adjusting the reaction temperature, which not only provides a simple method for the regulation of red and green light, but also complements scandium-based fluoride and broadened the application scope of scandium-based nanomaterials.