Short‐wave Infrared Photoluminescence Lifetime Mapping of Rare‐Earth Doped Nanoparticles Using All‐Optical Streak Imaging

Abstract The short‐wave infrared (SWIR) photoluminescence lifetimes of rare‐earth doped nanoparticles (RENPs) have found diverse applications in fundamental and applied research. Despite dazzling progress in the novel design and synthesis of RENPs with attractive optical properties, existing optical systems for SWIR photoluminescence lifetime imaging are still considerably restricted by inefficient photon detection, limited imaging speed, and low sensitivity. To overcome these challenges, SWIR photoluminescence lifetime imaging microscopy using an all‐optical streak camera (PLIMASC) is developed. Synergizing scanning optics and a high‐sensitivity InGaAs CMOS camera, SWIR‐PLIMASC has a 1D imaging speed of up to 138.9 kHz in the spectral range of 900–1700 nm, which quantifies the photoluminescence lifetime of RENPs in a single shot. A 2D photoluminescence lifetime map can be acquired by 1D scanning of the sample. To showcase the power of SWIR‐PLIMASC, a series of core‐shell RENPs with distinct SWIR photoluminescence lifetimes is synthesized. In particular, using Er3+‐doped RENPs, SWIR‐PLIMASC enables multiplexed anti‐counterfeiting. Leveraging Ho3+‐doped RENPs as temperature indicators, this system is applied to SWIR photoluminescence lifetime‐based thermometry. Opening up a new avenue for efficient SWIR photoluminescence lifetime mapping, this work is envisaged to contribute to advanced materials characterization, information science, and biomedicine.


Characterization
Structural Characterization.The crystallinity and phases of the core and core-shell rare-earth doped nanoparticles (RENPs) were determined via X-ray powder diffraction analysis on a Bruker D8 Advance Diffractometer (USA) using Cu Kα radiation (=1.5418Å).The morphology and size distribution of the core and core-shell structures were further investigated by transmission electron microscopy (TEM, Philips Tecnai 12, USA).The particle size was determined from TEM images using ImageJ software with a minimal set size of 100 particles.
Optical Characterization.Upconversion and downshifting spectra of oleate-capped RENPs in hexane were obtained at room temperature under the excitation of a 980-nm laser (MDL-SN-980-10W, CNI, China).Laser power and power density were about 490 mW and 8.0 W/cm 2 , respectively.All spectra were measured in a quartz cuvette of 1 cm optical path, filled with 2 mL of RENPs at 10 mg/mL concentration.The upconversion emission was recorded with an Avaspec-ULS2048L spectrometer (Avantes, The Netherlands).Stray light from the excitation source was Then, () is computed and used to fit the experimental result.
Figure S5 shows the photoluminescence lifetime extraction.The excitation pulse width was measured to be 200 μs. pulse () was produced after filtering the noise and cleaning the background (Figure S5a).In addition, the static slit image was averaged in the  direction (see an example in Figure 2e in Main Text) to produce a line profile (Figure S5b).Using the shearing relation [i.e., 97.6 μs/pixel (see Section 2.2 in Main Text)], the spatial pixels were converted to time bins, which produced  slit ().As an example, the normalized average photoluminescence intensity decay curve of Gd:Er@Gd (see Figure 3b in Main Text) and the fit are plotted in Figure S5c.Its corresponding semi-log plot is shown in Figure S5d.The lifetime of Gd:Er@Gd was determined by the fitted () that gave the highest R-squared value.For this sample, its photoluminescence lifetime was determined to be 3.59 ms (with R 2 = 0.9821).Finally, the semilog plots of the normalized average photoluminescence intensity decay of Lu:Er@Lu, and Yb:Er@Y RENPs (see Figure 3b in Main Text) are shown in Figures S5e-f.

Figure S4 .
Figure S4.Quantification of spatial resolution of SWIR photoluminescence lifetime imaging microscopy using an all-optical streak camera (PLIMASC).(a) Edge spread function extracted from an edge on a USAF resolution target.Error bar: standard deviation.(b) Line spread function produced from (a) with a Gaussian fit.FWHM: Full width at half maximum.

Figure S5 .
Figure S5.Determination of photoluminescence lifetime for Gd:Er@Gd RENP samples.(a) Normalized excitation pulse profile.(b) Averaged spatial profile of the slit.(c) Measured photoluminescence intensity decay of Gd:Er@Gd with the fit.(d) As (c), but plotted in the logarithmic scale.(e)-(f) As (d), but showing the results of Lu:Er@Lu (e) and Yb:Er@Y (f).