Simultaneous enhancement of near infrared luminescence and stability of Cs2AgInCl6:Cr3+ double perovskite single crystals enabled by a Yb3+ dopant

Abstract

Broadband near infrared (NIR) emission materials are of interest for various applications including non-destructive biomedical imaging. In this work, ytterbium ions (Yb³⁺) were successfully doped into Cs₂AgInCl₆:Cr³⁺ (CAIC:Cr³⁺) double perovskite single crystals (DPSCs) by a facile hydrothermal method. Under 365 nm excitation, the co-doped CAIC:Cr³⁺,Yb³⁺ DPSCs showed broad NIR emission ranging from 800 to 1400 nm, which spanned the NIR-I (700–900 nm) and NIR-II (1000–1700 nm) bio-windows, with an emission band at 1000 nm and a full-width at half maximum (FWHM) of 188 nm. It is found that Yb³⁺ ion doping could effectively improve the photoluminescence (PL) performance of CAIC:Cr³⁺ DPSCs. Compared to the photoluminescence quantum yield (PLQY) of 22.5% for the single doped CAIC:Cr³⁺, the co-doped CAIC:Cr³⁺,Yb³⁺ DPSCs show a higher PLQY of ∼45%, which is attributed to the synergistic effect of reduced non-radiative recombination due to defect passivation and increase in crystallinity, and energy transfer (ET) of self-trapped excitons (STEs) to Cr³⁺. As a demonstration of applications, NIR pc-LEDs were fabricated by combining the as-synthesized NIR-emitting phosphor CAIC:Cr³⁺,Yb³⁺ with InGaN UV chips (λ_em = 365 nm) and used to image veins in a palm and for night vision using a NIR camera. The results suggest that the synthesized CAIC:Cr³⁺,Yb³⁺ DPSCs have great potential in biological applications.