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.