Influência de tratamento térmico nas propriedades estruturais e ópticas de nanocristais de LaF3 co-dopado com Yb3+/Er3+

Abstract

In this work, we have investigated the role of heat treatment on the structural and spectroscopic properties of Rare-earth Er3+ and Yb3+ co-doped Lanthanum Fluoride (LaF3) nanocrystals. To this study, two sets of samples were prepared: In the first one we fixed the Yb3+ and Er3+ concentrations at 5 and 20 mol%, respectively, and it was carried out heat treatment after synthesis at the temperatures of 60 (without treatment), 300, 400, 500, 600, 700, 800, and 900 oC; in the second set of samples, we fixed the Yb3+ concentration at 10mol% and the heat treatment temperature at 500 oC and the Er3+ concentration was varied. To the structural characterization XRD, FT-IR, SEM, TEM, EDX and Raman measurements were carried out, while to the optical characterization luminescence in the visible and infrared regions were performed. All the analyses were carried out aiming the best sample to photonics applications with LaF3 nanocrystals. From the results, it was verified, increasing the temperature of heat treatment, an improvement in the LaF3 matrix crystalline structure and an increment in the luminescence intensity. However, for treatment temperatures over 500 oC a new crystalline phase was observed, inducing modification in the emission spectrum shape and, therefore, pointing out that the maximum temperature to heat treatment keeping the LaF3 structure is 500 oC. From the luminescence data, it was found an improvement of the emission with the treatment temperature and the sample treated at 500 oC was considered as the best LaF3 matrix. Regarding the results varying the Er3+ concentration, keeping fix the Yb3+ at 10 mol%, to Er3+ concentrations over to 2 mol% the emission bands intensity diminished due to concentration quenching caused in Er3+ ions. As a result of the analyses, the LaF3 nanocrystals that present a higher luminescence intensity and keeping the crystalline phase are those thermally treated at 500 oC and co-doped with 10 mol% of Yb3+ and 2.0 mol% of Er3+. The results obtained and presented in this dissertation open perspectives to several other researches and to use the current matrix to many photonics applications.