Coordination Geometry-Dependent Multi-Band Emissionand Atypically Deep-Trap-Dominated NIR PersistentLuminescence from Chromium-Doped Aluminates

摘要

An abnormal trap distribution and coordination geometry-dependent multibandemission are discovered in chromium-doped aluminates. The multi-bandand broadband persistent luminescence from 650–1100 nm peaking at 688and 793 nm from Cr3+-doped SrAl12O19 is systematically studied via structuraland spectroscopic analysis. Solid state nuclear magnetic resonance allows thevisualization of various coordination configurations in SrAl12O19, thus offeringthe possibility of tailoring the local geometry of the emission center to triggerthe control of the spectral parameter. Deep tissue ex vivo and in vivo imagingin mice both demonstrate that multi-band-emissive SrAl12O19:Cr3+ shows superior,high-quality near-infrared (NIR) bio-imaging in the biological transparencywindow compared to single band-emissive (with emission only at 688 nm)SrAl2O4:Cr3+, although SrAl2O4:Cr3+ has a higher luminescent intensity andlonger duration at 688 nm. Moreover, by measuring the thermoluminescencespectra the driving force of carrier release is discovered to be only from thedeep trap (the depth is > 1 eV), which is different from the generally acceptedshallow-dependent afterglow-emitting process. These findings pave the wayfor opening a vista of possible avenues for the enhancement of signal-to-noiseratio, the improvement of imaging quality, as well as the understanding of thetrapping and de-trapping process in long-persistent phosphors.