Banca de DEFESA: LUCELMA PEREIRA DE CARVALHO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : LUCELMA PEREIRA DE CARVALHO
DATE: 26/07/2021
TIME: 09:00
LOCAL: Programa de Pós-Graduação em Ciência de Materiais
TITLE:

Modeling of the Continuous Bright White Light Emissions by Energy Upconversion in Nanomaterials

KEY WORDS:

energy upconversion processes; white light; lanthanide ions

PAGES: 132
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:

Light emissions by upconvertion are processes in which lower energy photons are converted into higher energy photons. For example, excitation in the near infrared (NIR) region causes emissions in the visible region. These processes have several applications ranging from photovoltaics and lighting to nanomedicine, which arise great interest. In the last decade, a bright white light emission with a continuous spectrum was observed when exciting some materials, in particular, metal oxides, with high power density (laser) sources at the NIR region. The origin of this phenomenon is not yet established, which is the motivation for the development and implementation of a quantitative model. This model was based on the power balance equation in which the energy absorbed from the excitation beam is dissipated by heat transfer (thermal conduction), by internal heating (thermal capacity) and by thermal emission of white light (blackbody type). The numerical solution of the differential equation obtained in the model was successfully implemented and provided results without the approximations used in the analytical solutions. Thus, the temporal dependence of temperature and of the continuous broad bright white light emission by energy upconversion in (nano)materials were obtained and compared with experimental observations and data. All the main features of these continuous bright white light emissions were explained and quantified by the analytical and numerical results. In particular, the dependence of the integrated emission intensity on excitation source power, on the particle size and sample porosity and doping, on the ambient pressure and temperature, as well as the existence of a power density threshold of the excitation source and the non-exponential temporal decay of white light emission. It has been shown the reasons for the white light emissions obtained by upconversion are so bright and so intense, similar to incandescent bodies. The results obtained and their comparisons with experimental data suggest that the proposed model has been validated and describes quantitatively all the features of this process, and can be used to design new, more efficient materials and improve experimental conditions.

BANKING MEMBERS:
Externo à Instituição - Luís António Ferreira Martins Dias Carlos - UA
Interno - 1129726 - CID BARTOLOMEU DE ARAUJO
Presidente - 1134371 - RICARDO LUIZ LONGO