In-situ synthesis of chalcogenides nanocristals (Te0, CdS) in tellurites and phosphates glasses for photonics applications.

Author(s)

Renato Grigolon Capelo

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2020-06-19

Examining board members

Danilo Manzani; Valmor Roberto Mastelaro; Laudemir Carlos Varanda

• Advisor: Danilo Manzani

Abstract

<span style=\"font-weight: 400;\">The work presents the study of the reduction of Te<span style=\"font-weight: 400;\">4+<span style=\"font-weight: 400;\"> to Te<span style=\"font-weight: 400;\">0<span style=\"font-weight: 400;\"> in tellurite glasses doped with PbS and PbO/ZnS and seeks to induce, in a controlled manner, this redox process through the microfabrication technique using a pulsed laser on a femtosecond scale, with the goal of produce a planar waveguide. The tellurite glass samples were synthesized by varying the matrix composition and the dopants concentration and their thermal and structural properties were determined through various characterization techniques, such as differential scanning calorimetry (DSC), X-ray diffraction (XRD), Raman scattering spectroscopy, transmission electron microscopy (TEM), selected area electronic diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). The tellurite glasses doped with sulfides showed, in most samples, brown or black color (darkening effect). After analysis by Raman spectroscopy and SAED, the presence of Te<span style=\"font-weight: 400;\">0<span style=\"font-weight: 400;\"> in the samples was found, indicating that the S<span style=\"font-weight: 400;\">2-<span style=\"font-weight: 400;\"> ions cause the Te<span style=\"font-weight: 400;\">4+<span style=\"font-weight: 400;\"> reduction in the vitreous matrix, causing the darkening effect. The study of tellurium reduction in the vitreous matrix becomes very important and promising, since the controlled reduction of tellurium can generate changes in the refractive index (waveguides) and/or darkening of the sample (data storage and photosensitive materials). Thus, the femtosecond laser microfabrication technique was used in transparent samples in order to achieve a localized reduction of Te<span style=\"font-weight: 400;\">4+<span style=\"font-weight: 400;\"> in the volume of the glass. The work also investigates the formation of quantum dots (QDs) of CdS in phosphate-based oxyfluoride glasses and their respective photoluminescent properties. Absorption, emission and excitation spectra were obtained, and the results indicate the formation of QDs in the matrix. However, it was not possible, with the methods employed in this work, to control the formation and growth of CdS QDs. (AU)

• FAPESP's process: 18/16407-6 - Tellurite glasses containing PbS quantum dots: synthesis, characterization and photoluminescence investigations
• Grantee: Renato Grigolon Capelo
• Support Opportunities: Scholarships in Brazil - Master