Fig. 4: Mechanistic study of SrF₂:Pr³⁺.

a Photographs of SrF₂:0.5%Pr³⁺ powder and SrF₂:0.5%Pr³⁺ embedded in different polymers, including epoxy resin (ER), polydimethylsiloxane (PDMS), silicon gel (SG) and polyurethane (PU), under mechanical action. b Persistent luminescence (PersL) decay curve of SrF₂:0.5%Pr³⁺ after stoppage of 5-min X-ray irradiation. Inset: enlarged PersL signal upon stimulation of external force. c Photographs of SrF₂:0.5%Pr³⁺ upon single- and multiple-sliding during the PersL process. d Thermoluminescence (TL) curves of SrF₂:0.5%Pr³⁺ before and after grinding for 20 min. e Mechanoluminescence (ML) spectra of SrF₂:0.5%Pr³⁺ after different X-ray exposure dose. f Normalized TL and ML intensities of SrF₂:0.5%Pr³⁺ as a function of X-ray irradiation dose. Source data are provided as a Source Data file.