Persistent luminescence nanothermometers

Persistent phosphorescence nanoparticles emitting in the red and near-infrared spectral regions are strongly demanded as contrast nanoprobes for autofluorescence free bioimaging and biosensing. In this work, we have developed Sr₄Al₁₄O₂₅:Eu²⁺, Cr³⁺, Nd³⁺ nanopowders that produce persistent red phosphorescence peaking at 694 nm generated by Cr³⁺ ions. This emission displays temperature sensitivity in the physiological temperature range (20–60 °C), which makes these nanoparticles potentially useful as fluorescence (contactless) nanothermometers operating without requiring optical excitation. Nd³⁺ ions, which act as shallow electron traps for the red Cr³⁺ persistent emission, also display infrared emission bands, extending the fluorescence imaging capability to the second biological window. This unique combination of properties makes these nanoparticles multifunctional luminescent probes with great potential applications in nanomedicine.