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 NaYF₄:Er³⁺@NaYF₄ 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 ²H_11/2 -> ⁴I_15/2 and ⁴S_3/2 -> ⁴I_15/2 transitions of Er³⁺, respectively. It is verified that the intensity ratio of ²H_11/2 -> ⁴I_15/2 to ⁴S_3/2 -> ⁴I_15/2 transitions of Er³⁺ increases exponentially with rising temperature from 298 to 323 K, in line with the Boltzmann distribution. Therefore, the core-shell structure of NaYF₄:Er³⁺@NaYF₄ 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. © 2025 Wiley-VCH GmbH