Sínteses e caracterizações óptica e estrutural de nanopartículas de LaF3:Yb3+/Ho3+e LaF3:Yb3+/Tm3+ e cerâmicas transparentes de Y2O3:Eu3+e Y2O3:Tm3+

Abstract

Rare-earth ions co-doped lanthanum fluoride (LaF3) nanoparticles (NPs) were synthesized and the effect of different annealing temperatures investigated. We have also investigated the thermo-optical properties of Tm3+ and Eu3+ doped Y2O3 transparent ceramics. The LaF3:Yb3+/Ho3+ and LaF3:Yb3+/Tm3+ NPs were treated thermally by 3 hs at 300, 500, 700, and 900 °C and then characterized with respect to crystalline structures, sizes, shapes, presence of other crystalline phases and luminescent properties. From the experimental results, optimization of optical and structural properties were obtained for the thermal treatment at 500 °C while maintaining the LaF3 crystalline phase. However, it was observed the formation of lanthanum oxifluoride (LaOF) under thermal annealing at 900 °C, with higher luminescence in the near infrared, which makes this host to deserve further study. It was also synthesized LaF3 NPs varying the Tm3+ and Ho3+ ions concentrations with fixed Yb3+ one and these samples were thermally treated at 500 and 900 °C by 3 hs. The 1.2, 1.47, 1.8, and 2 μm emissions behaviors of Tm3+ and Ho3+ ions were investigated, in order to obtain the best concentrations for these emissions in these two hosts: LaF3 and LaOF. We also synthesized Yb3+/Tm3+ and Yb3+/Ho3+ co-doped LaF3 using nitrate and chloride precursors and these samples were annealed at 500 and 900° C to observe what occurs in the structural, morphological, and optical properties of the LaF3 and LaOF. As a result, no significant difference was observed in their structural and optical properties, thus facilitating the use of nitrate and chloride precursors for further researches using these hosts. Another very interesting and promising material is the yttrium oxide (Y2O3) transparent ceramics. In this case, we investigated using the thermal lens technique, conventional spectroscopy of luminescence and temporal dynamic, the thermal and optical properties of Y2O3:Tm3+ and Y2O3:Eu3+. The thermal properties obtained were: thermal diffusivity ��=26.06x10-3cm2/s, thermal conductivity ��=5.8 W/m.K, and the temperature coefficient of the optical path length change ����⁄=2.978x10-6K-1. Small values for D and k were obtained in comparison to those of the literature, and this was attributed to the grain size of the investigated ceramics. The luminescence decays along with the thermal lens spectroscopy results were complementary to a complete characterization of the Y2O3:Tm3+ ceramics, enabling obtaining the fluorescence quantum efficiency of the Tm3+ 3F4 level emitting at 1.8 μm, which was estimated at η1=0.84.