Near infrared light-controlled release of payloads from ultraviolet-sensitive (UV-sensitive) polymer hydrogels or nanocarriers is one of the most promising strategies for biotherapy. Here, we propose the concept of light activation of NaYF4:20%Yb,2%Tm nanocrystals (NCs). NaYF4:20%Yb,2%Tm NCs are synthesized by a solvothermal method. Effective upconversion luminescence from NaYF4:20%Yb,2%Tm NCs excited by a continuous wave (CW) 980 nm laser is obtained. The NaYF4:20%Yb,2%Tm NCs are then used as a