Research Digest 31resolution and more accurate signal localizations owing to the reduced light scattering at longer wavelength. These research results serve new ideas of designing inorganic NIR persistent phosphor probes for the new-generation autofluorescence-free in vivo biomedical imaging.Fig. 1. (a) Absorption spectrum and emission spectrum of LAO:Nd and LAO:Nd-Sm, respectively showing the potential energy transfer possibility due to the spectrum overlapping; (b) PLE spectra (λem=1080 nm) of LAO with and without Nd3+ co-doping proving the energy transfer process from Cr3+ to Nd3+; (c) Comparison between PL under excitation (λex=405 nm) and PersL after ceasing excitation showing identical spectrum with the same optical transitions from Cr3+ and Nd3+; (d) Persistent luminescent decay curves monitoring Cr3+ and Nd3+ emission bands showing intense NIR PersL last for at least 2 hours. (e) luminescent mechanism with energy levels of conduction-band, valence-band, Cr3+, Nd3+ and Sm2+ in vacuum referred binding energy (VRBE) diagram of LAO perovskite host.Fig. 2. (a) 775 short-pass (SP) filter and 810 long-pass (LP) filters are used upon pork meat for monitoring the PersL imaging by Si CCD camera (b) 910 long-pass (LP) filter is used upon pork meat to have a clear comparison of Si detector that only able to monitor the NIR imaging at NIR-I window while InGaAs detector able to monitor the NIR imaging at NIR-II window with higher light penetration and spatial resolution.References1) J. Xu, D. Murata, Y. Katayama, J. Ueda and S. Tanabe, J. Mater. Chem. B. 5 (2017) 6385.2) J. Xu, D. Murata, J. Ueda, B. Viana, S. Tanabe, Inorg. Chem. 57 (2018) 5194.3) J. Xu, S. Tanabe, J. Lumin. 205 (2019) 581.4) J. Xu, M. Back, S. Tanabe, “Chapter 11” of Phosphor Handbook (3rd edition)., CRC press (2022) 363 (56 pp).5) J. Xu, S. Tanabe, A.D. Sontakke, J. Ueda, Appl. Phys. Lett. 107 (2015) 081903.Nd3+ Persistent Luminescence at 1.06 μm in Perovskites for Excitation-Free Bioimaging Jian XU1. Outline of ResearchPerovskite with a general formula of ABX3, named after the Russian mineralogist L. Perovski, is one of the most important material families with remarkable properties, and plays key roles in various applications. In particular, perovskites are considered as very flexible luminescent matrices with two types of cation sites able to accommodate different luminescent activators, e.g., lanthanide (Ln) ions at the A site and/or transition metal (TM) ions at the B site, leading to various perovskite phosphors with attractive luminescent properties. Recently, we have developed a new perovskite persistent phosphor of LaAlO3 (LAO) with intense deep-red PersL of Cr3+ at 734 nm for several hours, in which co-doping with Sm3+ could act as an efficient electron trap to enhance the Cr3+ PersL over 35-fold [1]. Although deep-red or NIR PersL is very weak or even invisible to human’s visual perception, it possesses reduced light scattering and minimal absorption coefficient compared with ultraviolet (UV) and visible lights, which can be used for in vivo biomedical imaging [2] and night-vision surveillance. Especially for biomedical imaging, NIR persistent phosphors in nanoscale charged by excitation light before injecting into small animals could give intense PersL without in-situ excitation. The exclusion of external illumination contributes to the non-autofluorescence and non-heating effects, distinguished from real-time laser excitation used in the conventional photoluminescence (PL) or fluorescence imaging, and thus improve the signal-to-noise ratio remarkably [3,4]. 2. Research ActivitiesIndicated from the absorption spectrum of Nd3+ and emission of Cr3+ in LAO perovskite as shown in Fig. 1(a), energy transfer process occurs from Cr3+ to Nd3+, which is also confirmed by the exist of Cr3+ excitation bands at ~410 and 550 nm attributed to the transitions from the 4A2 ground state to 4T1 and 4T2 excited states of Cr3+ ions, respectively, when monitoring Nd3+ emission at ~1080 nm in Fig. 1(b). After ceasing UV excitation, the PersL spectrum of LAO:Nd-Cr-Sm is almost identical with PL (Fig. 1(c)), which suggests that Sm3+ acts as electron trapping center, and Cr3+ acts as PersL center as well as energy donor, while Nd3+ acts as energy acceptor generating PersL at 908 nm, 1078 nm and 1341 nm due to the Nd3+: 4F3/2→4I9/2, 11/2, 13/2 transitions for the NIR-I/II biological windows [5] as the mechanism demonstrated in the VRBE diagram in Fig. 1(e). Persistent decay curves monitoring Cr3+ and Nd3+ bands are shown in Fig. 1(d), which indicates that the Nd3+ PersL in the NIR-II window is comparable with that of Cr3+ PersL in the NIR-I window of ZnGa2O4 spinel.Simple demontration of in vitro imaging using LAO:Nd-Cr-Sm pellet is shown in Fig. 2. The ceramic pellet is covered by 1 cm thickness raw pork meat and the PersL after pre-charging by UV light is selectively monitored by Si and InGaAs cameras using 775 short-pass (monitoring Cr3+ emission), 810 long-pass (monitoring Nd3+ emission in NIR-I window) and 990 long-pass (monitoring Nd3+ emission in NIR-II window). Both Cr3+ and Nd3+ emission can be detected over 10 min thanks to this unique autofluorescence-free imaging technology. Moreover, compared with the Cr3+ emission, the Nd3+ emission matching with the sensitivity curve of InGaAs camera can achieve higher spatial
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