We propose what we believe is a novel optical thermometry strategy (FIR-Ex) based on the fluorescence intensity ratio (FIR) between two radiations associated with the same emission peak but different excitation wavelengths, in contrast to the traditional approach (FIR-Em), which depends on the FIR at varying emission wavelengths. The temperature-dependent FIR within the FIR-Ex strategy arises from the different charge/energy evolution routes, rather than the distribution of thermally coupled levels within the FIR-Em strategy. Considerable diversity in thermal behaviors and luminescence mechanisms was demonstrated by analyzing the 618 nm red emission in Pr3+-doped congruent LiNbO3 (Pr:CLN) under 360 and 463 nm excitations. The temperature sensitivity was further improved via Mg2+ codoping due to the optimization of charge dynamics and energy transfer processes. Given its wide detection scope, relatively high absolute sensitivity at low temperature, and high tunability of temperature sensitivity, the FIR-Ex strategy is promising for developing optical temperature-sensing materials with high performance.