Lanthanide luminescence nanothermometers (LNTs) present microscopic, extremely delicate, and visualizable optical indicators for reporting temperature info, which is especially helpful in biomedicine to realize exact analysis and remedy. Nonetheless, LNTs with environment friendly emissions on the long-wavelength area of the second and the third near-infrared (NIR-II/III) organic window, which is extra beneficial for in vivo thermometry, are nonetheless restricted. Herein, we current a lanthanide-doped nanocomposite with Tm3+ and Nd3+ ions as emitters working past 1200 nm to assemble a twin ratiometric LNT. The cross-relaxation processes amongst lanthanide ions are employed to determine a method to reinforce the NIR emissions of Tm3+ for bioimaging-based temperature detection in vivo. The twin ratiometric probes included within the nanocomposite have potential in monitoring the temperature distinction and warmth switch on the nanoscale, which might be helpful in modulating the heating operation extra exactly throughout thermal remedy and different biomedical functions. This work not solely supplies a robust device for temperature sensing in vivo but additionally proposes a way to construct high-efficiency NIR-II/III lanthanide luminescent nanomaterials for broader bio-applications.