Persistent Luminescence Ratiometric Thermometry at the Nanoscale

Persistent luminescence (PersL), characterized by sustained photon emission from certain material systems after the cessation of external light excitation, demonstrates great promise in temperature sensing due to the absence of background autofluorescence and thermal effects induced by real‐time excitation. However, previous research only achieves PersL thermometry in bulk materials, which is unsuitable for applications requiring nanoscale precision, such as life sciences. To address this challenge, a nanothermometer capable of temperature measurement in PersL mode is developed. A rationally designed NaYF 4 :Er 3+ @NaYF 4 core‐shell nanostructure exhibits hour‐long green PersL upon X‐ray charging. The two PersL lines, with central emission wavelengths at 528 and 545 nm, originate from the 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions of Er 3+ , respectively. It is verified that the intensity ratio of 2 H 11/2 → 4 I 15/2 to 4 S 3/2 → 4 I 15/2 transitions of Er 3+ increases exponentially with rising temperature from 298 to 323 K, in line with the Boltzmann distribution. Therefore, the core‐shell structure of NaYF 4 :Er 3+ @NaYF 4 provides an accurate PersL‐based nanothermometer, which holds significant potential for precise temperature measurement within biological tissues and at the single‐cell level, thereby enabling advanced thermal sensing in biomedical research.