Optical switching a photon-avalanche-like mechanism in NdAl₃(BO₃)₄ particles excited at 1064 nm by an auxiliary beam at 808 nm

In recent years, an unconventional excitation of trivalent neodymium ions (Nd3+) at 1064 nm, not resonant with ground-state transitions, has been investigated with the unprecedented demonstration of a photon-avalanche-like (PA-like) mechanism, in which the temperature increase plays a fundamental role. As a proof-of-concept, NdAl3(BO3)4 particles were used. A consequence of the PA-like mechanism is the absorption enhancement of excitation photons providing light emission at a broad range covering the visible and near-infrared spectra. In the first study, the temperature increase was due to intrinsic nonradiative relaxations from the Nd3+ and the PA-like mechanism ensued at a given excitation power threshold (Pth ). Subsequently, an external heating source was used to trigger the PA-like mechanism while keeping the excitation power below Pth at room temperature. Here, we demonstrate the switching on of the PA-like mechanism by an auxiliary beam at 808 nm, which is in resonance with the Nd3+ ground-state transition 4I9/2→{4F5/2,2H9/2}. It comprises the first, to the best of our knowledge, demonstration of an optical switched PA, and the underlying physical mechanism is the additional heating of the particles due to the phonon emissions from the Nd3+ relaxation pathways when exciting at 808 nm. The present results have potential applications in controlled heating and remote temperature sensing.