Rare earth luminescent materials have attracted extensive attention in the biomedical field as noncontact temperature monitoring devices with microscopic resolution due to their properties in the visible and near-infrared regions. At the application level, it is required to have a certain temperature monitoring capability in the near-infrared region II window to enhance the tissue penetration depth. Here, two kinds of YOFs: Er3+, Yb3+ were prepared by co-precipitation and hydrothermal method, and the luminescence was enhanced by ion doping. An Er3+-based ratiometric nanothermometer of ⁴F9∕2→4I15∕2 (672nm, upconversion luminescence) to ⁴I13∕2→4I15∕2 (1580nm/1566nm, NIR II downshifting luminescence) were designed with the Stark energy level. When doped with 2% Zn2+, the relative temperature sensitivity of YOF prepared by co-precipitation method was improved from 0.30% ∘C−1 (30^∘C) to 0.59% ∘C−1 (30^∘C), expanding its use as a temperature monitoring device possibility. The temperature sensitivity of YOF prepared by hydrothermal method was 1.01% ∘C−1 (30^∘C). Finally, the NIR II luminescence of the prepared nanothermometer was used as a control for temperature monitoring of heating sites in mice. The results showed that it can distinguish heating site from control site and no significant cytotoxicity or damage to the tissues was revealed, indicating its broad prospects in the biomedical field and other temperature monitoring scenarios in the future.