High performance NIR-I to NIR-II emission of a Cr3+-doped Cs2NaLuCl6 phosphor with an IQE and EQE of up to 92.9% and 60.75%

Abstract

Presently, there is a need to expand the near-infrared (NIR) emission range, especially in the bio-transparent window, to improve the internal quantum efficiency and external quantum efficiency, and to minimize the shortcomings of luminescence properties. In this work, an ultra-broadband NIR emission Cr³⁺-doped Cs₂NaLuCl₆ all-inorganic metal halide perovskite phosphor was synthesized by a grinding–sintering method. Under 300 nm excitation, Cs₂NaLuCl₆:Cr³⁺ phosphors exhibited ultra-broadband NIR emission of 800–1400 nm, which covers nearly the entire NIR-I (700–1000 nm) and NIR-II (1000–1400 nm) regions; the emission peaked at around 960 nm, with a full width at half maximum of ∼182 nm. Noticeably, the internal- and external-quantum efficiencies of the optimized Cs₂NaLuCl₆:Cr³⁺ phosphor were as high as ∼92.9% and ∼60.75%, respectively. We showed through analysis and simulation that the weak crystal field strength is conducive to increasing the odd term of the crystal field, and therefore it partially released the restriction imposed by the parity prohibition law and improved the energy absorption efficiency of Cr³⁺. As the size of the phosphor approaches the wavelength of NIR luminescence, the apparent Mie scattering effect starts to take effect, which enhances the light extraction of NIR luminescence in the radial direction.