Site-related near-infrared luminescence in MAl12O19 (M = Ca, Sr, Ba):Fe3+ phosphors

Intense and broad near-infrared (NIR) photoluminescence (PL) peaks locating at 777, 808 and 810 nm is observed for BaAl12O19 (BA6):1%Fe3+, CaAl12O19 (CA6):1%Fe3+ and SrAl12O19 (SA6):1%Fe3+, respectively. Electron paramagnetic resonance (EPR) spectra show that Fe3+ ions substitute for the different types of Al3+ sites simultaneously. Meanwhile, the luminescence of Fe3+ in MAl12O19 (M = Ca, Sr and Ba) are ascribed to octahedral Fe3+. In addition, the site symmetry of Fe3+ in CA6/SA6 is lower compared with BA6, deduced from the photoluminescence excitation (PLE), EPR and Fourier-transform infrared (FT-IR) spectra. These phosphors can be considered as good candidates for the applications in the field of high-resolution bioimaging.