Abstract The design of advanced materials often reveals how apparent imperfections, such as structural defects or impurities, can be transformed into functional advantages. In insulating oxide matrices, the controlled introduction of dopant ions is the first step toward efficient photoluminescence. Later, the engineering of additional defects, often detrimental for photoluminescence, gives rise to unique capabilities for optical energy storage and persistent luminescence. Initially driven by biomedical applications, nanomaterials currently occupy a central role in persistent phosphor research. However, elaboration processes allowing to preserve their nanoscale usually involve poor control over their crystallinity, leading to performance behind that of bulk materials. Developing nanophosphors with well‐defined morphology and energy levels engineered for tailor‐made and efficient energy storage presents a significant materials challenge. Yet once again, what seems a limitation may prove to be a powerful opportunity. By exploiting the nanoscale to engineer energy storage in an unprecedented manner, persistent nanophosphors can open a new era in advanced optical materials. This perspective highlights how emerging applications, progress in nanoscale synthesis, surface engineering, and integration into advanced architectures are opening the path toward multifunctional, application‐ready materials. Altogether, the nanoscale offers a transformative avenue that can enable persistent nanophosphors to outperform their bulk counterparts.
Castaing et al. (Tue,) studied this question.