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

• Intense 700–850 nm NIR emissions in MAl12O19 (M = Ca, Sr, Ba):1%Fe3+ has been obtained.
• The NIR emissions can be ascribed to the octahedral Fe3+ sites.
• The site symmetry of Fe3+ in CA6 and SA6 may be lower than that in BA6.
• The phosphors may be potentially applied in the high-resolution bioimaging.

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.

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