The well-formed high quality -NaYF4:Er3+/Tm3+, Yb3+ microcrystals with near/mid-infrared (NIR/MIR) emission are synthesized by the solvothermal method. Obvious 1.4m, 1.8m emissions, and 1.5m emission are observed in as-prepared -NaYF4:Tm3+, Yb3+ and -NaYF4:Er3+, Yb3+ microcrystals, respectively. To obtain MIR emission, the as-prepared -NaYF4:Er3+, Yb3+ microcrystals are heat-treated at different temperature schedule and atmosphere, it demonstrates there is great effect on the morphology and crystal structure when heat-treated at different temperature, while little effect under different heat-treated atmosphere. Subsequently, after heat-treatment at 575 degrees C in air, owing to the efficient elimination of internal defects and partly surface hydroxyl/citrate groups, an obvious 2.7m MIR emission is successfully detected in heat-treated -NaYF4:Er3+, Yb3+ microcrystals for the first time.