Desempenho da excitação em anti-stokes em amostras de NdxY1.00- xAl3(BO3)4 decoradas com nanopartículas metálicas

Abstract

Rare-earth ions have been increasingly studied in the literature due to their unique optical properties. In this work, conducted during the author’s master’s studies, we explored various optical and thermal effects in NdxY1.00-xAl3(BO3)4 samples decorated with metallic nanoparticles. Initially, we excited these samples at 808 nm, a resonant transition of neodymium contained in the micrometric particles of NdxY1.00-xAl3(BO3)4, promoting the transition from the ground state 4I9/2 to 4F5/2 + 2H9/2 of neodymium. Thanks to the rich configuration of neodymium's energy levels, we observed a wide band of upconversion and downconversion emissions, with spontaneous emissions ranging from 530 nm to 1100 nm. The laser excitation itself induces intrinsic heating due to the non-radiative relaxation pathways caused by the proximity of energy levels, elevating ions to more excited states and suppressing typical emissions from the 4F3/2level, such as 4F3/2 → 4I9/2 (900 nm), 4F3/2 → 4I11/2 (1064 nm), and 4F3/2 → 4I13/2 (1320 nm). Temperature exerts a quenching effect on these emissions at wavelengths shorter than the excitation laser wavelength. However, rather than converting all the energy into heat, part of it is used to promote ions from the 4F3/2 state to higher energy levels, resulting in emissions at wavelengths higher than those of the excitation laser photons. Moreover, decoration with metallic nanoparticles causes an increase in temperature due to the excitation of the nanoparticles' vibrational modes, acting as an additional heat source and enhancing upconversion through thermal excitation to levels above 4F3/2. In a second case, the samples were excited at a non-resonant wavelength with neodymium’s ground-state transitions, characterizing anti-Stokes excitation. The energy difference required to complete the transition from 4I9/2 to 4F5/2 is provided by phonon annihilation in the host matrix, and as the number of phonons increases with temperature, the process becomes more efficient. Due to the excitation of vibrational modes of metallic nanoparticles on the surface of the submicrometric particles of NdxY1.00-xAl₃(BO₃)₄ (x = 0.10, 0.20, and 1.00), additional heating occurs, enhancing the anti-Stokes process at 1064 nm. As a result, a significant improvement is observed in emissions between 600 and 880 nm. Given the considerable enhancement of anti Stokes processes in silver-decorated NdxY1.00-xAl3(BO3)4 microparticles compared to undecorated ones, it is expected that this approach could be applied to other samples. The results of this work were published in Optical Materials X under the title “Metallic nanoparticles-decorated NdxY1.00-xAl3(BO3)4 sub-micrometric particles to enhance anti Stokes excitation performance.”