Temperature triggering a photon-avalanche-like mechanism in NdAl3(BO3)4 particles under excitation at 1064 nm

Abstract

Photon avalanche (PA) is a fascinating mechanism for exciting trivalent rare-earth ions (REI3+). It occurs when cross-relaxation mechanisms provide a non-zero population at a lower excited state. Then, photons that are nonresonant with ground-state transitions can be increasingly absorbed from this level. PA has been demonstrated with some REI3+-doped materials under specific excitation wavelengths and temperature regimes. Here the PA-like was observed on NdAl3(BO3)4 particles at some fixed temperature values (within 23 ◦C ≤ T ≤ 215 ◦C), while the excitation power was increased. In this study, the PA-like is associated to a cross-relaxation mechanism [ 4 F3/2, 4 I9/2] → [ 4 I15/2, 4 I15/2]. After multiphonon emissions, the population of Nd3+ ions at the 4 I11/2 state doubles at every iteration, a process followed by a resonant excited-state absorption ( 4 I11/2 → 4 F3/2). In this case, the excitation power threshold decreased threefold. In a second round of experiments, we demonstrate for the first time the triggering the PA-like mechanism by increasing the temperature (27 ◦C ≤ T < 35 ◦C) at a fixed excitation power (1064 nm, cw). We foresee applications of the present results in optical thermometry, hyperthermia treatments, super-resolution imaging, and the development of super-sensitive sensors.