Banca de DEFESA: RODRIGO FERREIRA DA SILVA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : RODRIGO FERREIRA DA SILVA
DATE: 11/03/2024
TIME: 08:30
LOCAL: Auditório do IF-UFAL
TITLE:

Effects of Nd3+ concentration on energy upconversion due to a photon avalanche-type mechanism in crystalline NdxY1.00- xAl3(BO3)4 particles under non-resonant excitation at 1064 nm

KEY WORDS:

Avalanche de fótons; íons terras-raras trivalentes; espectroscopia

PAGES: 108
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUBÁREA: Física da Matéria Condensada
SPECIALTY: Prop. Óticas e Espectrosc. da Mat. Condens; Outras Inter. da Mat. com Rad. e Part.
SUMMARY:

Trivalent rare earth ions have been shown to be extremely efficient in absorbing and emission of different wavelengths. This is because the optically active electrons are not the outermost, which weakens the ion bond when doped into a host material, due to partial shielding of the 4f state. In this text, the fluorescent efficiency of Nd3+ (neodymium) in NdxY1.00-xAl3(BO3)4 particles under a non-resonant Anti-Stokes type excitation (1064 nm) starting from the ground state to the 4F3/2 level was shown. Even with a non-resonant excitation, intensities were observed in the very broad photoluminescent spectrum, from visible to infrared, which is explained by the photon avalanche (AF) type excitation mechanism, which very efficiently favored the level population. 4F3/2 along with phonon annihilation to initially populate the 4F3/2 level. In the interaction between an excited ion (4F3/2) and another in the ground state (4I9/2), the excited ion performs a cross-relaxation (non-radiative) interacting with an ion in the ground state in such a way that the first relaxes from the level 4F3/2 to 4I15/2 and the second is excitedly promoted from 4I9/2 to 4I15/2. Due to the proximity to the lower levels, these ions relax non-radiatively to the 4I13/2 and 4I11/2 levels. Once at the 4I11/2 level, ions can absorb radiation from the excitation beam that is resonant with the 4I11/2 🡪 4F3/2 transition. Thus, an ion initially excited at the 4F3/2 level by a
low probability at room temperature, takes two ions to the 4F3/2 state and after the sequence of events: phonon-assisted ground state absorption; cross relaxation; non-radiative relaxations and resonant excited state absorption. The two ions at the 4F3/2 level can transfer energy to two neighbors in the ground state and take four ions to the 4F3/2 level. The repetition of this set of events leads to an excitation that follows a geometric progression of excited ions, abruptly increasing the absorption of photons at 1064 nm. With large numbers of ions at the 4F3/2 level we can observe transitions that characterize upconversion and downconversion of energy covering the
visible and infrared spectrum. The influence of neodymium concentrations for different samples was also investigated, and a strong dependence on cross-relaxation was found for the photon avalanche mechanisms, due to the proximity of the ions, and with this, an energy looping mechanism was proposed for concentrations of 5% to 20% of Nd3+, and for concentrations greater than 20%, the photon avalanche is established. The results of this dissertation are published in the journals: Applied Physics Letters with the title “Photon-avalanche-like upconversion in NdAl3(BO3)4 nanoparticles excited at 1064nm” and Optical Materials with the title “Energy-looping and photon-avalanche-like phenomena in NdxY1 .00-xAl3(BO3)4 powders excited at 1064 nm”.

COMMITTEE MEMBERS:
Presidente - 1695829 - ANDRE DE LIMA MOURA
Externo(a) à Instituição - ANDERSON STEVENS LEONIDAS GOMES
Externo(a) à Instituição - TASSO DE OLIVEIRA SALES