Cr3+/Er3+ co-doped LaAlO3 perovskite phosphor: a near-infrared persistent luminescence probe covering the first and third biological windows
We have developed a novel persistent phosphor of LaAlO3 perovskite doped with Er3+, Cr3+, and Sm3+ (LAO:Er–Cr–Sm), which exhibits long persistent luminescence (PersL) at 1553 nm due to the Er3+:4I13/2 → 4I15/2 transition as well as at 734 nm due to the Cr3+:2E(2G) → 4A2(4F) transition. The intense near-infrared (NIR) PersL bands from Cr3+ and Er3+ match well with the first (NIR-I, 650–950 nm) and third (NIR-III, 1500–1800 nm) biological windows as well as response curves of commercial Si and InGaAs detectors. The photon emission rates of Cr3+ (6.06 × 1016 cps sr−1 m−2) and Er3+ (3.69 × 1016 cps sr−1 m−2) at 60 min after ceasing ultraviolet (UV) illumination were comparable with that of the widely used ZnGa2O4:Cr3+ red persistent phosphor (5.41 × 1016 cps sr−1 m−2). Furthermore, we also show the first in vitro autofluorescence-free imaging through pork tissues by Si/InGaAs cameras monitoring Cr3+/Er3+ PersL, and demonstrate that the Er3+ emission can achieve higher spatial resolution than the Cr3+ emission due to the reduced light scattering at longer wavelengths. It is indicated that this material can act as a promising bio-probe for in vivo optical imaging, especially in the NIR-III biological window.