Fig. 3: Dynamics and imaging of UCC in Gd₃Ga₅O₁₂:Cr³⁺ phosphor.

a Schematic of trapping and detrapping in the UCC process (see the text for further details). b Double-logarithmic plots depicting thermoluminescence intensities (I) versus power densities (P) of a 450 nm laser. The square curve depicts the I-P relationship measured with a fixed illumination duration of 10 s, while the circle curve illustrates the I-P under a constant dose of 0.3 W·s·mm⁻². The upper inset provides a profile of the portable laser engraver equipped with a 450 nm diode laser module and XY-axis guide rails. The lower inset displays afterglow images captured at 267 °C following phosphor charging using the laser engraver at −196 °C. The three letters were recorded using the laser module at varying power densities with a constant 0.3 W·s·mm⁻² dose. The illumination parameters for the three images were 1.2 W·mm⁻² for 0.25 s, 6 W·mm⁻² for 0.05 s, and 30 W·mm⁻² for 0.01 s, respectively. c Afterglow images with stereoscopic and depth effects using UCC, recorded under the same imaging conditions as in (b). d Resolution advantage of UCC, shown with a smaller circle compared to traditional UV methods. Images taken with a 0.6-s shutter