Luminescence properties of Cr 3+ -doped near-infrared emissive fluoroyttrates for light-emitting diodes.

In this work, a series of Cr 3+ -doped A 2 NaYF 6 (denoted as ANYF:Cr; A = K, Rb, and Cs) fluoroyttrate double-perovskites with broad blue excitation and near-infrared (NIR) emission bands were prepared using a high-temperature solid-state reaction method. The physicochemical and spectroscopic properties of the as-prepared products, including crystal structure, bandgap, morphology, luminescence behaviour and optical performance, were studied in detail. The results show that the Cr 3+ activators undergo a decreasing crystal field in ANYF in the direction from K to Cs, yielding a red shift of the emission peak position from 758 to 786 nm, whilst the full-width-at-half-maximum (FWHM) expands from 98 to 104 nm. By virtue of the broadband NIR emission, clear structural images of the tangerine section, mini LED flashlight and circuit board were obtained by merging the optimal RNYF:Cr phosphor on a blue InGaN chip, implying its potential use in light-emitting diodes for non-destructive testing.