Li5 Zn8 Ga5 Ge9 O36 : Cr3+ , Ti4+ : A Long Persistent Phosphor Excited in a Wide Spectral Region from UV to Red Light for Reproducible Imaging through Biological Tissue.

Near-infrared (NIR) long-persistent phosphors (LPPs) have emerged as a potential solution for bio-imaging applications over the past few years. However, there are enormous challenges regarding their in situ application based on their dependence on short-wavelength excitation. In this paper, we report a multi-spectral excited NIR LPP, Li5 Zn8 Ga5 Ge9 O36 : 1.5 % Cr3+ , 0.5 % Ti4+ , which overcomes the limitations of functional processes in biological tissues and other complex systems. This LPP exhibits a high luminescent intensity and a long emission duration in the NIR region (700-800 nm). The applicability of this phosphor to tissue imaging is demonstrated experimentally. Its persistent luminescence (PersL) can easily penetrate approximately 2 mm of pork flesh. More importantly, this phosphor can be re-charged in situ using a red LED or laser diode array to provide renewed NIR PersL for biological tissues, which is beneficial for long-term biological tissue imaging applications with high signal-to-noise ratios. Systematic investigations of the nature of energy traps and PersL mechanisms are also reported in this paper.