Photoluminescent properties of doped alkali borosilicate glasses

• Autor(a) principal: Almeida, Mário André Madeira de
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/34212
• topic: Tin Oxide; Copper Oxide; UV-Downconversion; Luminescent solar concentrators; Alumina-borosilicate glass matrix; Thin-Films; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

This project was developed with the purpose to achieve innovative solutions of UV light down conversion. Such was accomplished through the synthesis of photoluminescent glasses doped with tin oxide and copper oxide, also preliminary studies on the development of photoluminescent thin films based on the same elements was approached. Photoluminescent quantum yields and Stokes shift were taken as guidelines to evaluate the photoluminescent behaviour of the produced samples. The synthetic strategy applied for photoluminescent glass samples was systematic, it consisted on the insertion of a variable doping amount of each element over an alumina-borosilicate glass matrix which were prepared at high temperatures of 1400 ºC and 1550 ºC. Structural features were evaluated through SSNMR for 29Si, 11B, 23Na, and Raman spectroscopy, which showed that doping does not affect the network structural matrix. Dilatometry measurements were performed showing a negligible variation of the thermomechanical properties of the samples. Doping concentrations have revealed to be a key factor for the achievement of high quantum performances, where we have observed triplet state light emission derived from three emissive species. Its origin resides in Sn2+, Sn2+ aggregates and Cu+ species in the glass matrix. Tin oxide doped samples shown quantum efficiencies of 50% and 1.7 eV Stokes shift for 1.4% molar tin oxide concentration, while copper oxide doped samples present 58% quantum efficiency and large 3 eV Stokes shift for 0.14% molar concentration. Thin film deposition strategy was based on the identification of optimal conditions for the formation of copper and tin oxide crystalline phases. Results were evaluated through X-ray diffraction and Raman spectroscopy showing the formation of both crystalline phases over variable oxygen flow. A multi-layer thin film deposition was performed and diffusion was attempted through thermal treatment. Results indicate the formation of a protective SnO2 layer over the formation of Cu2O phase, increasing its thermal stability to 400 ºC.