Banca de DEFESA: TALITA JORDANNA DE SOUZA RAMOS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : TALITA JORDANNA DE SOUZA RAMOS
DATE: 28/07/2023
TIME: 09:00
LOCAL: Programa de Pós-Graduação em Ciência de Materiais
TITLE:

DISCRETE AND CONTINUOUS UPCONVERSION EMISSIONS IN OXIDES DOPED WITH LANTHANIDE IONS

KEY WORDS:

nanothermometry, manometry, energy transfer, photonic converters, incandescence, UC emission.

PAGES: 125
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:

In inorganic materials, based on or doped with lanthanides, energy upconversion (UC) luminescence can be mediated by different mechanisms, such as excited state absorption, energy transfer upconversion, and photon avalanche processes. However, these mechanisms lead to UC emission characterized by discrete spectra and, therefore, cannot explain the generation of white light characterized by continuous spectrum observed in pure, doped, or co-doped lanthanide oxides upon NIR excitation. In this thesis, we present our contribution to the elucidation of the mechanism that promotes the emission of white light, characterized by a continuous spectrum, upon excitation in the NIR, depending on the composition of the samples, thermal conductivity, distribution, and size of particles, as well as the conditions of excitation (wavelength, cycles, and excitation time). We elaborated a study of the photophysical behavior for mechanical mixtures of commercial oxides Gd2O3, Yb2O3 and Er2O3, and for synthesized nanoparticles with compositions: Yb2O3 and Er2O3 (pure); (Gd0,99Er0,01)2O3 and (Gd0,99Yb0,01)2O3 (doped); and (Gd0,89Yb0,10Er0,01)2O3 (co-doped), as a function of temperature, humidity, and pressure. The spectral and temporal behaviors observed for the emission characterized by broadband, namely, the fits of the emission in the visible region to the blackbody emission curve and the analysis of the temporal dynamics for different power densities (which show the patterns consistent with heating and cooling steps) suggest that the white light emission is of thermal origin. This is corroborated by the transition of the discrete to continuous UC emission caused by the optical heating of the sample. The synthesized nanoparticles (Gd0,89Yb0,10Er0,01)2O3 behave as primary luminescent thermometers (under NIR excitation) in the range of 299–363 K, using the Er3+ emission intensity ratio 2H11/2→4 I15/2/ 4S3/2→4 I15/2, and as a secondary luminescent thermometer in the range 1949–3086 K, based on the blackbody distribution curve of the observed white light emission. The results regarding the relationship between the temperature of the excitation region and the power density used to excite the sample will be useful for the development of theoretical models and for solving the differential equations that describe the emission of white light by laser heating.

COMMITTEE MEMBERS:
Presidente - 1130924 - OSCAR MANOEL LOUREIRO MALTA
Interno - 1129726 - CID BARTOLOMEU DE ARAUJO
Externo à Instituição - SIDNEY JOSE LIMA RIBEIRO - UNESP
Externo à Instituição - DANILO MANZANI - USP
Externa à Instituição - Verónica Cortés de Zea Bermúdez
Externo à Instituição - Luís António Ferreira Martins Dias Carlos - UA