Efficient Near-Infrared Luminescence with Near-Unity Photoluminescence Quantum Yield in Erbium-Doped Double Perovskites Cs₂NaYCl₆ under Green Light Excitation

Abstract

Lanthanide (Ln 3+ )-doped double perovskites to achieve near-infrared (NIR) emission have been demonstrated to be an effective strategy. However, these emitters generally exhibit low emission efficiencies, which limits further applications. Herein, we synthesized Er 3+ -doped Cs 2 NaYCl 6 via a hydrothermal reaction. Steady-state and transient fluorescence spectra show that there is a pronounced cross-relaxation between neighboring Er 3+ , thus boosting the NIR emission with a photoluminescence quantum efficiency (PLQE) of 93 ± 2% (NIR-II region ∼87%). Moreover, the ferromagnetic coupling can enhance the absorption intensity of Er 3+ ; thus, the strongest emission of Er 3+ -doped Cs 2 NaYCl 6 can be witnessed via direct excitation at 520 nm. The remarkable PLQE and ideal excitation wavelength make Cs 2 NaYCl 6 :Er 3+ an ideal candidate for the next generation of NIR light sources. In addition, Nd 3+ and Yb 3+ were also doped in Cs 2 NaYCl 6 successfully, and their respective PLQE values are 51 ± 3% and 30 ± 2%, respectively. Particularly, the emission intensity of Ln 3+ -doped Cs 2 NaYCl 6 at 440 K can maintain 103% (Er 3+ ), 91% (Nd 3+ ), and 112% (Yb 3+ ) of the initial emission intensity at 300 K. Their admirable properties enable us to demonstrate the application of as-synthesized compounds in night vision and nondestructive testing. Therefore, our findings make Ln 3+ -doped Cs 2 NaYCl 6 one of the most promising NIR emitters.