Six‐Photon Excited Self‐Trapped Excitons Photoluminescence in Lead‐Free Halide Perovskite

Abstract Multiphoton absorption (MPA) effects are suitable for biophotonic applications due to the long penetration depth and high spatial confinement. Compared with lead halide perovskites, relevant studies on MPA effects of lead‐free perovskites are still scarce, especially for the high‐order MPA effects. Herein, an all‐inorganic lead‐free Cs₂TeCl₆ perovskite crystal is reported that exhibits three‐ to six‐photon absorption (3PA to 6PA) effects over a wavelength range of 800–2200 nm. The results of steady and transient optical experiments indicate that the single‐ and multiphoton excited broadband orange emission in Cs₂TeCl₆ crystals is attributed to the self‐trapped excitons (STEs) recombination. What is more, the 6PA cross‐section (δ₆) has been determined to be 1.87 × 10⁻¹⁷⁴ cm¹² s⁵ photon⁻⁵ (at 1980 nm). As far as it is known, the high‐order 6PA effect is unprecedented in lead‐free perovskites, which paves the way for the future development of lead‐free perovskite high‐order multiphoton application.