Energy-looping and photon-avalanche-like phenomena in NdxY1.00-xAl3(BO3)4 powders excited at 1064 nm

Abstract

Recently, a photon-avalanche-like (PA-like) process based on trivalent neodymium ions (Nd3+) under an unconventional excitation at 1064 nm was demonstrated using stoichiometric NdAl3(BO3)4 particles. Although the Nd3+ can emit radiation at 1064 nm efficiently, they present very small absorption at this wavelength due to the absence of resonant ground-state transitions. However, phonon-assisted excitation (4I9/2 → 4F3/2 and/or 4I11/2 → 4F3/2) followed by cross-relaxation between one excited ion (4F3/2) with another at the ground state (4I9/2), and subsequent phonon emissions {4I15/2, 4I15/2 → 4I13/2, 4I13/2 → 4I11/2, 4I11/2}, provide two ions at the 4I11/2 state, from which can occur the resonant excited-state absorption to the 4F3/2 level. Reestablishing this sequence of events, the absorption of photons at 1064 nm can be greatly increased. Besides the emission around 880 nm (4F3/2 → 4I9/2), there are thermal excitations to upper-lying states, with subsequent emissions in the visible and near-infrared regions (480–2000 nm). Here, we investigate the role of the Nd3+ content on the PA characteristics in NdxY1.00-xAl3(BO3)4 particles with x ranging from 0.05 to 1.00. It is known that the replacement of Y3+ by Nd3+ into the YAl3(BO3)4 crystalline structure can introduce strong modifications of the lattice properties as well as in the photoluminescence characteristics, such as luminescence concentration quenching and broadening of spectral lines. Despite that, we observed, for low x (≤0.20), an energy-looping preceding the PA-like that ensues for x ≥ 0.40. It is associated to the proximity between the Nd3+ ions, fundamental to the electric dipole-electric dipole interaction responsible for the Nd3+ energy transfer {4F3/2, 4I9/2} → {4I15/2, 4I15/2}. We discuss the present results focusing on emerging technologies with development of ultra-sensitive thermal sensors.