Intense upconverted ultraviolet emission of Er³⁺ through confined energy transfer in Yb³⁺/Er³⁺ co-doped Rb₃InCl₆

Yb³⁺/Er³⁺ activated upconversion (UC) materials have been widely applied in many advanced technologies owing to their high UC efficiency in the visible region. However, it is challenging to achieve efficient ultraviolet (UV) UC luminescence (UCL) in Yb³⁺/Er³⁺ system, due to the dense energy levels of Er³⁺ that impose deleterious nonradiative relaxation. Herein, we report a strategy to liberate the UV-UCL of Er³⁺ based on the confined energy transfer in Yb³⁺/Er³⁺ co-doped 0D Rb₃InCl₆ with a low phonon energy and a large interionic distance. This facilitates the population of Er³⁺ at the ⁴G_11/2 state, which yields intense upconverted UV emission at 384 nm, with a much higher UV-to-green ratio (I₃₈₄/I₅₅₄ = 0.864) than that of traditional UC materials ( < 0.1). By leveraging the intense upconverted UV emission of Er³⁺, we demonstrate the application of Rb₃InCl₆:Yb³⁺/Er³⁺ nanocrystals as a NIR-to-UV transducer for NIR-triggered anion exchange of CsPbX₃ perovskite nanocrystals with high efficiency and good controllability. These findings offer an approach for the exploration of novel UC materials via energy transfer and crystal lattice engineering towards versatile applications.