Near-infrared downshifting emissions under a photon-avalanche-like excitation

Abstract

Photon-avalanche (PA) excitation of trivalent lanthanide ions is a fascinating mechanism in which the material is initially transparent to the exciting radiation. Through the participation of phonons from the host medium, some ions are promoted to an excited state. A series of cross-relaxation and excited-state absorption can double the number of excited ions with each iteration, leading to intense emissions. Although first reported many years ago, PA has since been utilized to generate upconversion emissions. Here, we leverage the richness of Nd³ ⁺ electronic structure to demonstrate, for the first time, downshifting emissions under PA excitation. As a proof-of-concept, PA-like excitation at 1064 nm of Nd³ ⁺ in NdAl₃(BO₃)₄ particle powders is demonstrated, resulting in emissions in the range of 1200–1800 nm, corresponding to Nd³ ⁺ electronic transitions. Recently, unprecedented applications of PA have been reported in super-resolution imaging, thermal sensors, and optical transistors based on light wavelengths below 1000 nm. Our findings extend the wavelength range of PA, opening up new possibilities for its application.