Investigation On Near-infrared Non-gallate Long Phosphorescent Materials

With the development of near infra-red （NIR） emission, detection technology, fluorescence imaging has drawn wide attention in biomedical applications, owing to its distinct merits of high sensitivity and non-invasiveness. The discovery of NIR persistent phosphors enables fluorescent probes to make a great progress over the last few years, since NIR persistent phosphors possess of the characters of what fluorescent probes should be. The characters of NIR persistent phosphors are as follows:（1） emission wavelengths lie in the region of biologically transparent window region （650-900 run and 1000-1400 nm）; （2） without real-time excitation of UV-vis removes the likelihood of auto-fluorescence/background noise, and thus a significant improvement in the signal-to-noise ratio and sensitivity is attained. So far, the Cr³⁺ doped NIR persistent phosphors exhibit excellent optical properties. However, most of the Cr³⁺ doped NIR persistent phosphors are gallate-based. Considering the high cost of gallates and the poor NIR persistent luminescence of non-gallates, we developed the NIR persistent luminescence of non-gallates by codoping rare earth ions through two ways. The details are as follow:1. Ce³⁺/Cr³⁺ co-doped LaAlO3 for near-infrared （NIR） long lasting phosphors were synthesized through solid-state reaction. Incorporation of Ce³⁺ ions into Cr³⁺-doped LaAlO3 significantly enhanced the NIR persistent luminescence by more than one order of magnitude compared with LaAlO3 doped with Cr³⁺. Detailed analysis of the photoluminescence, photoluminescence excitation, and Thermo-luminescence spectra, as well as the persistent decay behavior of Ce³⁺/Cr3³⁺ co-doped LaAlO₃, indicated that the improvement of NIR persistent luminescence at around 735 nm (Cr³⁺:2Eâ†'4A2 transition) is not only originated from a persistent energy transfer process from Ce³⁺ ions to Cr3* ions, but also attributed to the extra efficient traps created by incorporation of Ce³⁺ions. The current work develops an alternative approach toward the efficient NIR Cr³⁺-doped n on-gal late long persistence phosphors.2. The bright near infra-red （NIR） persistent ceramic discs of Zn2SnO4:Cr³⁺, Eu³⁺ were prepared by a solid state method and investigated in detail. The NIR emission （centred at 800 nm） of Cr3* is demonstrated to be enhanced by the energy transfer （ET） from Eu³⁺ions with the help of photoluminescence and photoluminescence excitation spectra. Besides, the analysis of persistent decay curves and thermo-luminescence spectra indicates that the Eu³⁺ ions acting as effective trap centers contributes to the significant improvement of Cr³⁺ NIR emission. Herein Eu³⁺ ions act both excellent sensitizers and effective trap centres in emission and persistent luminescence, respectively. This study develops an effective way to improve the MR luminescence and the NIR persistent luminescence of Zn₂SNO₄:Cr³⁺.