Highly Efficient STEs NIR‐II Broadband Emission in a Perovskite System and its Spectroscopy Applications

Efficient NIR emitting materials have important application value in phosphor‐converted light‐emitting diodes (pc‐LEDs), due to their high sensitivity of tissue composition responsiveness, and penetration depth (spatial resolution). In this work, a perovskite structure material CaSnO3 that can emit strong broad NIR light at the range of 850–1300 nm peaking at 1010 nm second biological window with a super large Stokes shift of 24463 cm−1 and a sensitive broad UV light response (λmax = 291 nm) by traditional high‐temperature solid‐state reaction that does not require additional doping ions is innovatively developed. Spectroscopic and theoretical calculations reveal that the NIR emission originates from self‐trapped excitons (STEs) enhanced by Jahn–Teller effect when Sn4+ is spontaneously reduced to Sn2+ and occupies the position of Ca2+ 8‐coordinate lattice. A prototype NIR‐II emitting LED device is successfully fabricated combining this perovskite CaSnO3 phosphor with UV 285 nm chip to evaluate its application value. This work provides a novel NIR‐II luminescent material, which is different from other doping types of systems, and STEs luminescence in perovskite has been achieved in the NIR‐II region for the first time, providing a new approach and choice for the development of NIR luminescent materials. Ultraviolet activated STEs broad NIR emission peaking at 1010 nm with large Stokes shift is achieved in the oxide perovskite matrix with the help of Jahn‐Teller distortion, when Sn4+ions self‐reduce to Sn2+ions and occupy eight‐coordination sites. A NIR‐II emitting LED device is successfully fabricated combining this oxide perovskite phosphor with UV chip to evaluate its application value.