Yao Xiao,Puxian Xiong,Shuai Zhang,Kang Chen,Shuhang Tian,Yongsheng Sun,Peishan Shao,Kexin Qin,Mikhail G. Brik,Shi Ye,Dongdan Chen,Zhongmin Yang
Developing deep-red to near infrared (NIR) materials with multi-mode luminescence is challenging, which has promising utilization in various applications such as stress sensing and dynamic signature anti-counterfeiting. Different to the mainstream non-centrosymmetric mechanoluminescence (ML), a centrosymmetric perovskite compound (MgGeO 3 : Mn 2+ ) ML material is reported. Deep-red to NIR light (600–800 nm) from Mn 2+ ion is confirmed, which is attributed to the strong crystal field within the [MgO 6 ] polyhedron. The stiffness tetrahedral units and large defect accommodating space within the host are favorable for both ML and persistent luminescence (PersL). Mn 2+ ion is the only luminescent center, which is confirmed by spectral characterizations. Based on diffuse reflectance spectra, thermoluminescence analysis and density functional theory calculations, the inherent relationship between PersL, ML and PL is further clarified in detail. Due to the formation of Mn Mg defects, shallow trap significantly become shallower after adding Mn 2+ ions. This study reports a Mn 2+ -doped deep-red to NIR ML phosphor, and further describes the PersL and ML mechanisms via defect engineering regulation. In general, this study may also open up a new approach for the development of efficient NIR ML materials, and show various potential applications such as in anti-counterfeiting and information encryption fields.
Near-infrared (NIR) persistent phosphors have attracted extensive research interest owing to their distinct wavelength features and self-sustained luminescence properties. However, the high-energy ultraviolet light that is consistently used to charge these phosphors has compromised some promising applications, especially for biomedical imaging. Herein, we have successfully utilized long-wavelength 635 nm red-light to achieve intense NIR persistent luminescence in a MgGeO3:Mn2+,Yb3+ phosphor. Seconds to minutes of 635 nm red-light charging can result in long-lasting NIR afterglow at around 680 nm for longer than 12 h. The photon trapping and detrapping processes in the MgGeO3:Mn2+,Yb3+ phosphor were investigated in detail by varying the 635 nm red laser output power and the excitation duration, which indicate that a two-photon upconversion charging process is responsible for NIR persistent luminescence upon red-light illumination. The red-light-charging capability and self-sustained NIR luminescence properties make this material perfectly suited to applications across a wide number of fields, such as acting as ideal optical probes for deep-tissue bio-imaging and developing optical data storage technology for information security systems.
In this paper, we have designed long afterglow luminescent MgGeO3:Mn2+,Yb3+,Li+ (MGO) nanoparticles in the first (NIR-I) and second (NIR-II) biological windows. Yb3+ ions served not only as the trap center to enhance the NIR-I long afterglow emission of Mn2+ at 680 nm, but also as an emitting center to produce a NIR-II long afterglow emission at ∼1000 nm. Furthermore, we have found the addition of Li+ can greatly increase the NIR-II afterglow emission of Yb3+ and the optimal amount of Mn2+, Yb3+ and Li+ was found to be 0.1, 0.5 and 0.5 mol%, respectively. The MGO nanoparticles synthesized using sol–gel methods showed a uniform morphology with a diameter of 50–100 nm, which were suitable for applications in bioimaging. More importantly, we have found MGO nanoparticles can be effectively excited to produce long persistent NIR-I and II luminescence using soft X-rays, suggesting that low dosage soft X-rays can also serve as a more powerful and deep tissue excitation source to recharge MGO nanoparticles. Furthermore, the MGO nanoparticles can also be re-excited to produce photo-stimulated emission under the irradiation of 650 and 808 nm NIR lasers. The in vivo imaging results have shown that MGO nanoparticles modified with folic acid (FA) can effectively realize super long-term targeted in vivo imaging of inflammation with a high sensitivity via recharging using soft X-rays and NIR lasers, which can provide not only an accurate diagnosis of inflammation, but also long-term monitoring of possible changes in the focus of inflammation in real time.
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