<p>Luminescent thermometry has become a research hotspot in recent years due to its advantages of high spatial resolution, fast response, and non-invasive nature. However, achieving high-performance temperature imaging requires both luminescent materials with high temperature sensitivity and efficient temperature imaging methods, which remains a significant challenge. In this study, a series of pure-phase rubidium germanate phosphors doped with manganese were synthesized and encapsulated into polydimethylsiloxane (PDMS) films to improve their chemical stability. The dramatic temperature-dependent luminescence behavior of Mn⁴⁺ in the Rb₂Ge₄O₉ matrix provides reliable and efficient methods for temperature sensing. The high-sensitivity temperature sensing capability of the Rb₂Ge₄O₉:0.002 Mn⁴⁺ fluorescent film has been confirmed, leveraging temperature-dependent emission intensity, luminescence decay lifetime, and time-resolved intensity ratio techniques. Notably, Rb₂Ge₄O₉:Mn⁴⁺ fluorescent film exhibits a strikingly high relative sensitivity of 17.03% K⁻¹ at 330 K in the time-resolved thermometry scheme, which is the highest relative temperature sensitivity within the physiological temperature range known to us. High-performance temperature imaging of the fluorescent film is achieved through the time-resolved intensity ratio strategy with a best practical temperature resolution of 0.08 K at 325 K. Furthermore, the temperature images of an operating nickel circuit with a line width of 20 under different working currents were recorded, showing a clear circuit microstructure and temperature gradient. These findings pave a novel path for realizing high-performance temperature imaging.</p>