Fig. 4: Investigation of temperature response mechanism of LIBRA.

a Schematic of LIBRA with enhanced sensitivity and the third near-infrared biological window (NIR-III) emission endowed by the optimized thin active shell doped with Yb³⁺ ions to achieve the energy migration (EM) of the lanthanide ion excited states across the core and shell layer of the nanocomposite and the environment quenching (EQ) by H₂O molecules of the excited states. b NIR luminescence spectra of LIBRA in solid powder and those dispersed in water at 10, 50, and 90 °C. c Luminescence intensity change of the emissions at 980 and 1550 nm of LIBRA in solid powder (980-Powder and 1550-Powder) and dispersed in water (980-H₂O and 1550-H₂O) at different temperatures. The intensities were normalized at 283 K to compare the changing behavior of different emissions. Data were presented as mean values based on three individual measurements (n = 3) by spectrometry. Error bars were defined as standard deviation. d Luminescence decay curves of emissions at 980 and 1550 nm of LIBRA@PEG with 50% Yb³⁺ in the shell at different temperatures in water (980-H₂O and 1550-H₂O) and in dimethylformamide (980-DMF and 1550-DMF). e Visible and NIR luminescence spectra of LIBRA@PEG with the inert shell thickness of 1.6, 3.7, and 12.4 nm in aqueous environment. f Luminescence intensity ratio change of the emissions at 1550 and 980 nm (I₁₅₅₀/I₉₈₀) of LIBRA@PEG with various inert shell thicknesses at different temperatures. The ratios were normalized at 283 K to compare the slopes of fitted curves of different nanocomposites. Data were presented as mean values based on three individual measurements (n = 3) by spectrometry. Error bars were defined as standard deviation. g Relative thermal sensitivity (S_r) of ratio (I₁₅₅₀/I₉₈₀) of LIBRA@PEG with 0 and 50% Yb³⁺ in the shell. h Luminescence intensity change of the emissions at 980 and 1550 nm of LIBRA@PEG with the active shell thickness of 0, 0.52, 1.45, 3.06, and 5.91 nm in aqueous environment. i Luminescence intensity ratio change of emissions at 1550 and 980 nm (I₁₅₅₀/I₉₈₀) of LIBRA@PEG with different active shell thickness at different temperatures. The ratios were normalized at 283 K to compare the slopes of fitted curves of different nanocomposites.