Broad Dual Emission by Codoping Cr3+ (d→d) and Bi3+ (s→p) in Cs2Ag0.6Na0.4InCl6 Double Perovskite

Abstract A phosphor emitting both white light and broad near‐infrared (NIR) radiation can simultaneously provide visual inspection and early signs of rotting of food products. The broad NIR emission is absorbed by the vibrational overtones of water molecules present in food items, providing the non‐invasive image contrast to assess the food freshness. Here we design a phosphor, namely, Cr 3+ ‐Bi 3+ ‐codoped Cs 2 Ag 0.6 Na 0.4 InCl 6 , that simultaneously emit warm white light and broad NIR (1000 nm) radiation with quantum yield 27 %. This dual emitter is designed by combining the features of s 2 ‐electron (Bi 3+ ) and d 3 ‐electron (Cr 3+ ) doping in a weak crystal field of the halide perovskite host. excitation of Bi 3+ , using a commercial 370 nm ultraviolet light‐emitting‐diodes (UV‐LED), yields both the emissions. A fraction of the excited Bi 3+ dopants emit the warm white light, and the other fraction transfers its energy non‐radiatively to Cr 3+ . Then the Cr 3+ de‐excites emitting broad NIR emission. Temperature dependent (6.4–300 K) photoluminescence in combination with Tanabe‐Sugano diagram show that the Cr 3+ experiences a weak crystal field ( =2.2), yielding the NIR emission. As a proof of concept, we fabricated a panel containing 122 phosphor‐converted LEDs, demonstrating its capability to inspect food products.