Lanthanide luminescence nanothermometers (LNTs) present microscopic, extremely delicate, and visualizable optical alerts for reporting temperature data, which is especially helpful in biomedicine to attain exact prognosis 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 to in vivo thermometry, are nonetheless restricted. Herein, we introduced 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 the 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 purposes. This work not solely gives a robust device for temperature sensing in vivo but additionally proposes a technique to construct high-efficient NIR-II/III lanthanide luminescent nanomaterials for broader bio-applications.