Enabling Efficient Mid‐Infrared Luminescence of Tm³⁺ in a Single Core–Shell Nanocrystal through Erbium Sublattice

Abstract

Mid‐infrared luminescence at around 1.8 μm has shown great potential in many frontier photonic fields. However, how to realize the 1.8 μm emission of Tm3+ with multiple pump wavelengths and in particular in nanosized hosts has remained a challenge so far. Herein, an erbium sublattice–based core–shell nanostructure is proposed to achieve the multiwavelength excitable mid‐infrared emission of Tm3+ at around 1.8 μm from its 3F4 → 3H6 transition. The core–shell engineering and cross‐relaxation help to improve the population of Er3+ at its 4I13/2 energy level and subsequent energy transfer to Tm3+ (3F4) for its efficient 1.8 μm emission upon 808, 980, and 1530 nm excitations. The modulation of energy‐transfer channels by codoping other rare‐earth ions shows that introducing a small amount of Ce3+ into the erbium sublattice can enhance the 1.8 μm emission of Tm3+ through favorable cross‐relaxation processes. Moreover, the 1.8 μm emission is further significantly enhanced by designing a core–shell–shell nanostructure with a NaYF4:Yb‐sensitizing interlayer, which is able to maximize the absorption of 980 nm excitation energy. These results provide a new conceptual nanosized model for mid‐infrared luminescent materials toward infrared biophotonics and microlasers.

Wavelength-Independent Pumping Mechanism and Spectroscopic Property of Upconversion Nanoparticles for Laser-Flexible Microscopic Bioimaging

“…Er 3+ ions can be excited by 808, 980, and 1530 nm laser beams (Figure S1). − Similarly, Tm 3+ ions were excited by 808, 1064, 1150, and 1208 nm laser (Figure S2). ,− Although Kasha’s rule is widely applicable to various luminescence processes, including UCL.…”