Polar state transitions are one of the most intriguing phenomena in relaxor ferroelectric research, motivating many phenomenological models and experimental analyses. In addition to many electrical techniques that permit the evaluation of characteristic temperatures, this manuscript shows that the changes in rare-earth luminescence properties can act as an alternative probe. Here, we explore the luminescence properties of erbium-doped PLMN–13PT (lanthanum-modified lead magnesium niobate–lead titanate) under temperature and electric field-induced polar state transitions. In analogy to the magnetism setups, four electric field conditions were carried out during the cooldown and heating procedures: no-field, poled, zero-field-cooled (ZFC), and field-cooled (FC). The intensities of visible Er3+ emissions 4S3/2 → 4I15/2 and 2H11/2 → 4I15/2 exhibit peculiar behavior at the freezing temperature (TF) for the no-field condition, as nonlinear to linear transition, and a maximization. In an external electric field, these features shift to higher temperatures for the poled condition, and the amplitude evolves with a higher slope below TF for ZFC. However, in the FC condition, the emissions behave similarly to the no-field case, indicating competition between the modes of depolarization. Our results show that rare-earth ion emissions correlate with the polar nanoregion dynamics and probe the ergodic, non-ergodic, and paraelectric transitions.